IN  MEMORIAM 
Edmund  O'Neill 


CHEMICAL  ANALYSIS  OF 
LEAD  AND  ITS  COMPOUNDS 


Chemical  Analysis  of 
Lead  and  Its  Compounds 


BY 


JOHN  A.  SCHAEFFER,  A.M.,  Ph.D. 

V ice-President  and  Chief  Chemist,  The  Eagle-Picher  Lead  Co. 

AND 

BERNARD  S.  WHITE 

A  •isistant  Chemist  and  General  Superintendent  of  the 
Joplin  Plant,  The  Eagle-Pic  her  Lead  Co. 


REVISED  AND  ENLARGED 
BY 

J.  H.  CALBECK,  A.M. 

Director  of  Research,  Tfte  E,agle-Pi*he*f  Lead  Co. 


THE  EAGLE-PICHER  LEAD  COMPANY 

JOPLIN  CHICAGO  NEW  YORK  PITTSBURGH 

ST.  LOUIS  CINCINNATI  PHILADELPHIA 

KANSAS  CITY  CLEVELAND  BALTIMORE 


COPYRIGHT,  1912 
COPYRIGHT,  1922 

IN  MEMOR1AM 


THE  EAGLE-PICHER  LEAD  COMPANY 


DEDICATED  TO 


who  died  April  26,  1920,  and  who  was  the  first  presi- 
dent of  The  Eagle-Picher  Lead  Company.  His 
constant  aim  throughout  life  was  the  development 
of  the  lead  industry.  Its  present  state  of  perfection 
is  largely  due  to  his  efforts  at  all  times  to  advance 
the  metallurgical  art,  as  it  relates  to  the  manufac- 
ture of  lead  and  its  compounds,  not  only  from  a 
humanitarian  standpoint,  but  also  as  a  growth 
along  sound  scientific  lines.  In  his  death  the  indus- 
try has  suffered  a  distinct  loss. 


PEEFACE  TO  SECOND  EDITION. 

The  demand  for  this  book  has  made  the  Second 
Edition  necessary.  The  book  continues  to  be  a 
compilation  of  standard  methods,  already  well 
known,  that  combine  accuracy  with  rapidity. 

Certain  revisions  and  additions  have  been  made 
that  should  increase  the  usefulness  of  the  book. 
A  method  of  calculating  percentage  of  composition 
of  Sublimed  White  Lead  by  J.  A.  Schaeffer  and  a 
rapid  method  for  analysis  of  copper  and  iron  in  red 
lead  and  litharge  by  B.  S.  White  are  also  included. 

March,  1922. 


PREFACE. 

A  review  of  the  literature  on  the  analysis  of 
lead  and  its  compounds  reveals  a  multiplicity  of 
methods,  many  of  which  are  of  little  value  in 
technical  work  of  today,  owing  to  the  many  opera- 
tions entailed  and  the  possibility  of  error  attend- 
ing every  lengthy  analysis.  The  laboratory  of 
today,  so  closely  connected  with  all  lines  of  manu- 
facture, must  control  through  chemical  analysis 
every  process  leading  from  the  raw  material  to 
each  finished  product.  It  demands  extreme  accu- 
racy coupled  with  rapidity  of  manipulation.  That 
the  best  methods  combining  these  salient  points 
are  not  in  general  use  in  many  laboratories  deal- 
ing with  lead  compounds  is  evidenced  from  the 
numerous  requests  for  such  which  continually 
reach  us. 

It  is  with  the  hope  that  the  methods  adopted  by 
the  leading  laboratories  in  the  lead  districts,  will 
prove  of  some  special  value,  that  this  work  is 
written.  In  it  will  be  found  certain  new  methods 
which  retain  exactness  with  considerable  conser- 
vation of  time  and  many  others  of  general  adop- 
tion. Should  it  aid  in  increasing  the  efficiency  of 
any  laboratory  practice  the  authors  will  feel  that 
its  mission  has  been  fulfilled. 

August,  1912. 


ix 


TABLE  OF  CONTENTS. 

Chapter  Page 

I   ANALYSIS  OF  LEAD  ORE 1 

II   SUBLIMED  WHITE  LEAD 9 

III  THE   LEAD   CONTENTS   OF  SUBLIMED    WHITE 

LEAD — A  CALCULATION 27 

IV  SUBLIMED  BLUE  LEAD 32 

V   ZINC  OXIDE 35 

VI   LITHOPONE 48 

VII  A  COLORIMETRIC  METHOD  FOR  THE  DETER- 
MINATION OF  COPPER  AND  IRON  IN  PIG 
LEAD,  LEAD  OXIDES  AND  LEAD  CARBONATE  59 

VIII   RED  LEAD  AND  ORANGE  MINERAL 66 

IX   LITHARGE 85 

X   BASIC  CARBONATE  OF  LEAD 89 

XI   ELECTROLYTIC  DEPOSITION  OF  LEAD 109 

XII   STANDARD  METHOD   OF  CHEMICAL  ANALYSIS 

OF  PIG  LEAD Ill 

XIII  STANDARD  METHODS  OF  CHEMICAL  ANALYSIS 

OF  SPELTER 125 

XIV  STANDARD  METHODS  OF  CHEMICAL  ANALYSIS 

OF  ALLOYS  OF  LEAD,  TIN,  ANTIMONY  AND 

COPPER 135 

XV   PHYSICAL  PROPERTIES  OF  PIGMENTS 148 

INDEX..  153 


CHEMICAL  ANALYSIS  OF 
LEAD  AND  ITS  COMPOUNDS 

CHAPTER  I 

ANALYSIS   OF  LEAD   OBES 

The  principal  ore  of  lead  which  will  be  encoun- 
tered by  the  analyst  is  ;Ga.lena<,  the,-£iblphide  of 
lead,  PbS.  In  certain" instances  Anglesite,  the 
sulphate  of  lead,  PbSO^,  and:  jC^rii&Hs;  the  car- 
bonate of  lead,  PbCO'a,  wiff  reach  the  laboratory 
for  examination.  The  constituents  usually  sought 
in  the  analysis  of  these  compounds  are  lead,  zinc 
and  silver,  though  at  times  the  iron  and  silicates 
present  must  be  determined.  The  value  of  the  ore, 
however,  will  depend  upon  the  content  of  lead,  zinc 
and  silver. 

The  ore  upon  reaching  the  laboratory  is  dried 
at  105°  C.  for  several  hours  and  then  pulped  so  as 
to  pass  through  a  100-mesh  sieve.  The  ore  is  then 
ready  for  examination. 

Ammonium  Molybdate  Method  for  the 
Determination  of  Lead 

Digest  one  gram  of  the  sample  with  15  c.c.  of  con- 
centrated nitric  acid  in  a  covered  beaker.  Boil  the 
solution  until  the  brown  fumes  of  the  oxides  of 

i 


2  Chemical  Analysis  of  Lead  and  Its  Compounds 

nitrogen  have  disappeared.  Add  6  c.c.  of  concen- 
trated sulphuric  acid  and  again  boil  until  the  heavy 
fumes  of  sulphuric  acid  are  evolved.  Allow  the 
solution  to  cool,  add  30  c.c.  of  water  and  boil.  Re- 
move the  beaker  from  the  hot  plate  and  allow  the 
solution  to  stand  at  least  four  hours,  preferably 
over  night.  Filter  the  solution,  washing  the  pre- 
cipitate by  decantation  three  or  four  times  to  com- 
pletely remove  the  iron.  The  filtrate  is  reserved 
for  the  determination  of  zinc. 

Wash  the  filter  paper  used  in  the  previous  filtra- 
tion with  75  c.c.  of  acid  .ammonium  acetate  solution 
made  up  in  tlie  following  irianner : 

AinmonilHh  'Hydroxide    (con- 
centrated)    95  c.c. 

Water 100  c.c. 

Acetic  acid  (80%) 125  c.c. 

Follow  this  washing  with  75  c.c.  of  hot  water, 
allowing  all  the  washings  to  be  caught  in  the  beaker 
containing  the  residual  lead  sulphate.  Boil  until 
complete  solution  has  been  effected  and  determine 
the  lead  volumetrically  in  the  hot  solution  by  titra- 
tion  with  standard  ammonium  molybdate  solution, 
as  given  under  the  Standardization  of  Ammonium 
Molybdate. 

Standardization  of  Ammonium  Molybdate 

Dissolve  8.67  grams  of  ammonium  molybdate  in 
one  liter  of  water.  Each  c.c.  of  this  solution  should 
be  equivalent  to  one  per  cent  of  lead,  when  a  one 


Analysis  of  Lead  Ores  3 

gram  sample  is  used.  Standardize  as  follows: 
Weigh  up  0.5  gram  pure  litharge.  Add  30  c.c.  hot 
water  and  32  c.c.  (80%)  acetic  acid.  Heat  to  boil- 
ing and  when  all  the  litharge  is  in  solution  add 
27  c.c.  con.  ammonium  hydroxide.  Dilute  to  200 
c.c.  with  hot  water,  boil  and  titrate  with  the  stand- 
ard ammonium  molybdate,  using  an  outside  indi- 
cator of  1  part  of  tannic  acid  in  300  parts  of  water. 
The  appearance  of  a  yellow  color  indicates  an  ex- 
cess of  ammonium  molybdate.  It  has  been  found 
that  a  correction  of  0.7  of  1  c.c.  of  the  titration  vol- 
ume must  be  deducted  as  a  blank  to  allow  for  the 
sensitiveness  of  the  reaction. 

The  following  precautions  must  be  observed  in 
carrying  out  this  method : 

Calcium  forms  a  more  or  less  insoluble  molyb- 
date, and  when  calcium  is  present  results  are  apt 
to  be  high.  However,  when  less  than  2  per  cent  of 
calcium  and  a  high  percentage  of  lead  are  present, 
there  appears  to  be  no  interference  from  the  cal- 
cium. This  method  is  only  applicable  to  samples 
containing  more  than  20  per  cent  of  lead.  Should 
a  lower  percentage  of  lead  be  present  it  may  be 
determined  by  the  bichromate  method  or  weighed 
as  the  sulphate. 

Bichromate  Method  for  the  Determination 
of  Lead 

Treat  one  gram  of  the  sample  with  concentrated 
nitric  acid,  evaporate  to  dryness  and  cool.  Take 


4  Chemical  Analysis  oj  Lead  and  Its  Compounds 

up  the  residue  with  75  c.c.  of  a  solution  made  up  in 
the  following  manner: 

Acetic  acid  (80%) 255  c.c. 

Ammonium   hydroxide    (con- 
centrated)   150  c.c. 

Water 595  c.c. 

Boil  gently  for  a  short  time,  filter,  and  wash  well 
with  boiling  water.  Treat  the  filtrate  with  sufficient 
neutral  potassium  bichromate  to  precipitate  all  the 
lead  and  boil  until  the  lead  chromate  has  become  an 
orange  yellow  color.  Filter  and  wash  with  hot 
water  until  all  the  uncomhined  potassium  bichro- 
mate is  removed.  The  above  conditions  must  be 
carefully  watched,  as  a  slight  deviation  may  result 
in  the  formation  of  a  basic  lead  chromate.  The 
ready  formation  of  this  compound  has  prevented 
the  general  adoption  of  this  method.  Dissolve  the 
lead  chromate  in  dilute  hydrochloric  acid  (1:1), 
using  as  little  of  the  acid  as  possible. 

Titrate  the  chromic  acid  present  in  the  solution 
with  ferrous  ammonium  sulphate,  having  an  iron 
value  of  0.00202,  using  a  two  per  cent  solution  of 
potassium  ferricyanide  as  an  outside  indicator.  It 
is  necessary  to  deduct  0.5  of  one  c.c.  of  the  ferrous 
ammonium  sulphate  standard  solution  for  each  75 
c.c.  of  solution  used,  as  the  amount  required  for  the 
sensitiveness  of  the  reaction. 

To  prepare  the  ferrous  ammonium  sulphate  solu- 
tion dissolve  14.19  grains  c.  p.  ferrous  ammonium 
sulphate  in  a  liter  of  distilled  water.  A  small  scrap 
of  aluminum  foil  in  the  bottle  prevents  oxidation. 


Analysis  oj  Lead  Ores  5 

Calculation 

The  percentage  of  lead  may  be  determined  di- 
rectly by  multiplying  the  number  of  c.c.  of  ferrous 
ammonium  sulphate  used  by  the  factor  0.25.  This 
factor  is  determined  by  the  following  equations : 

K2Cr207  +  6  Fe  S04  +  8H2S04  -  2KHSO4  + 
Cr2(S04)3  +  3  Fe2(S04)3  +  7  H20. 
2  PbCr04=2  Pb  +  Cr206. 
Cr2  Oo  is  equivalent  to  6  Fe. 
2  Pb  is  equivalent  to  6  Fe. 
Therefore  the  factor  from  iron  to  lead  equals 

414. 60_  1  9.7 
335.04- 

Strength  of  ferrous  ammonium  sulphate  solu- 
tion equals  0.00202  Fe. 

0.00202X1.237=0.0025  equals  grams  of  lead  per 
c.c.  of  solution. 

Then  the  number  of  c.c.  of  ferrous  ammonium 
sulphate  used  multiplied  by  0.25  or  divided  by  4 
gives  the  percentage  of  lead  present  when  a  one 
gram  sample  is  used. 

The  lead  may  be  calculated  directly  from  the 
amount  of  iron  titrated  by  using  the  factor  1.237. 


Sulphate  Method  for  the  Determination 
of  Lead 

Details  for  the  gravimetric  determination  of  lead 
as  sulphate  are  given  under  the  analysis  of  Basic 
Carbonate  of  Lead  on  page  89. 


6  Chemical  Analysis  of  Lead  and  Its  Compounds 

Determination  of  Zinc 

Add  8  grams  of  ammonium  chloride  to  the  filtrate 
and  washings  from  the  lead  sulphate  precipitate. 
Render  the  solution  alkaline  with  ammonium 
hydroxide,  boil,  filter  off  any  iron  hydroxide  which 
is  precipitated,  wash,  dissolve  this  precipitate  in 
dilute  hydrochloric  acid,  reprecipitate  with  ammo- 
nium hydroxide,  boil,  filter  and  thoroughly  wash. 
Combine  the  filtrates,  neutralize  the  ammonium 
hydroxide  present  with  hydrochloric  acid  and  add 
an  excess  of  6  c.c.  of  concentrated  hydrochloric 
acid.  Dilute  to  about  250  c.c.,  heat  to  about  80° 
C.,  add  a  few  drops  of  saturated  sodium  thiosul- 
phate  solution.  Titrate  with  standard  potassium 
ferrocyanide  as  outlined  under  the  Standardization 
of  Potassium  Ferrocyanide,  using  as  an  outside 
indicator  a  5  per  cent  uranium  nitrate  solution. 

Standardization  of  Potassium  Ferrocyanide 

Dissolve  10  grams  of  pure  metallic  zinc  in  hydro- 
chloric acid.  The  solution  is  made  up  to  1  liter  and 
a  volume  equivalent  to  0.2  gram  is  measured  out. 
The  remaining  solution  may  be  kept  for  restand- 
ardizing  the  ferrocyanide  solution  which,  on  stand- 
ing, appears  to  change  from  time  to  time.  In  place 
of  using  the  standard  zinc  solution,  0.5  gram  of  pure 
zinc  oxide  may  be  used  for  each  standardization. 

The  ferrocyanide  solution  is  made  by  dissolving 
43.26  grams  of  crystallized  potassium  ferrocyanide 
and  7  grains  of  sodium  sulphite  in  a  liter  of  water. 
The  addition  of  the  sodium  sulphite  helps  to  keep 


Analysis  of  Lead  Ores  7 

the  ferrocyanide  solution  at  a  constant  strength. 
One  c.c.  of  this  solution  will  be  equal  to  approxi- 
mately 0.01  gram  of  metallic  zinc. 

The  indicator  is  prepared  by  dissolving  uranium 
nitrate  in  water  until  a  faint  yellow  color  is  pro- 
duced. A  5  per  cent  solution  will  usually  give  a 
good  end  reaction. 

The  acid  solution  containing  0.2  of  a  gram  of  zinc 
is  made  faintly  alkaline  with  ammonium  hydrox- 
ide, using  litmus  paper  to  determine  the  end  point. 
Reacidify  faintly  with  hydrochloric  acid  and  add 
6  c.c.  of  concentrated  hydrochloric  acid  in  excess. 
Dilute  to  about  250  c.c.  and  heat  to  about  80°  C. 

The  solution  is  titrated  with  the  ferrocyanide 
solution  until  a  few  drops  of  the  zinc  solution  give 
a  brownish  tinge  to  the  uranium  nitrate  indicator 
on  the  spot  plate.  As  the  end  point  develops  slow- 
ly, it  is  well  to  examine  each  spot  after  standing 
for  a  brief  time.  The  first  one  developing  a  brown 
tinge  is  taken  as  the  end  point.  It  is  necessary 
to  make  a  correction  for  the  amount  of  ferrocy- 
anide solution  required  to  develop  a  brown  color 
in  the  uranium  nitrate  indicator  when  zinc  is 
absent.  This  correction  is  deducted  from  the  total 
amount  of  ferrocyanide  solution  used  and  will  usu- 
ally run  about  0.5  of  a  c.c. 

Determination  of  Silver 

The  treatment  of  lead  ores  for  the  assay  of 
silver  depends  wholly  upon  the  nature  of  the 
ere.  The  various  fluxes  used  for  the  formation 


8  Chemical  Analysis  oj  Lead  and  Its  Compounds 

of  the  lead  button  cannot  be  outlined  here,  owing 
to  their  number ;  the  analyst  desiring  to  make  this 
determination  may  readily  determine  a  method 
of  reduction  by  consulting  any  standard  text  on 
assaying. 


CHAPTER  II 

SUBLIMED  WHITE  LEAD 
(Basic  Sulphate  of  Lead) 

An  average  approximate  analysis  of  sublimed 
white  lead  as  commercially  placed  upon  the  mar- 
ket should  show  about  78.5  per  cent  of  lead  sul- 
phate, 16  per  cent  of  lead  oxide  and  5.5  per  cent 
of  zinc  oxide. 

Analysis 
Total  Sulphates 

Mix  0.5  gram  of  the  sample  with  3  grams  of 
sodium  carbonate  in  a  beaker.  Treat  the  mix- 
ture with  30  c.c.  of  water  and  boil  gently  for 
ten  minutes.  Allow  to  stand  for  four  hours. 
Dilute  the  contents  of  the  beaker  with  hot  water, 
filter  off  the  residue  and  wash  until  the  filtrate  is 
about  200  c.c.  in  volume.  Reject  the  residue.  By 
this  reaction  all  the  lead  sulphate  is  changed  to 
carbonate,  the  sulphate  being  transposed  into 
sodium  sulphate,  which  is  found  in  the  filtrate. 

Acidulate  the  filtrate  with  hydrochloric  acid  and 
add  an  excess  of  about  2  c.c.  of  the  acid.  Boil, 
and  add  a  slight  excess  of  barium  chloride  solu- 
tion (12  c.c.  of  an  8  per  cent  solution).  When  the 
precipitate  has  well  settled,  4  hours  or  preferably 
over  night,  filter  on  an  ashless  filter,  wash,  ignite 
and  weigh  as  BaS04.  Calculate  the  BaSO4  to 

9 


10        Chemical  Analysis  of  Lead  and  Its  Compounds 

PbS04  by  using  the  factor  2.6,  when  a  half  gram 
sample  is  used. 

Weight  of  BaS04  X  1.3  equals  weight  PbS04. 

On  0.5  gram  sample  factor  BaS04  to  PbS04=2.6. 

Lead 

Molybdate  Method1 

Dissolve  1  gram  of  the  sample  in  100  c.c.  of  an 
acid  ammonium  acetate  solution  made  up  as  fol- 
lows: 

Eighty  per  cent  acetic  acid 125  c.c. 

Concentrated      ammonium      hy- 
droxide    95  c.c. 

Water 100  c.c. 

Add  this  solution  hot  and  dilute  with  about  50 
c.c.  of  water.  Boil  until  dissolved. 

Dilute  to  200  c.c.  and  titrate  with  standard  am- 
monium molybdate  solution,  spotting  out  on  a 
freshly  prepared  solution  of  tannic  acid.  Details 
of  this  method  are  given  under  the  Analysis  of 
Lead  Ores. 

Ammonium  molybdate  is  a  slightly  variable  salt, 
but  a  solution  containing  8.67  grams  per  liter  usu- 
ally gives  a  standard  solution : 

1  c.c.  equals  0.01  gram  Pb. 
Standardize  against  pure  PbO  or  pure  PbS04. 

Bichromate  Method 

Treat  the  sample  as  above  described  until  dis- 
solved. If  the  solution  is  not  quite  clear,  filter. 

^Modification  of  Low's  Method.  Technical  Methods  of  Ore 
Analysis,  Low,  p.  149. 


Sublimed  White  Lead  11 

Add  to  the  filtrate  an  excess  of  neutral  potassium 
bichromate  solution.  Boil  until  the  lead  chromate 
has  become  an  orange  yellow  color  and  stand  in  a 
warm  place  until  the  precipitate  has  settled.  Filter 
on  a  Gooch  crucible,  wash  thoroughly,  ignite  below 
a  red  heat  and  weigh  as  PbCr04. 

The  PbCr04  may  be  estimated  volumetrically  by 
titrating  the  chromic  acid  present.  For  this 
method,  dissolve  the  lead  chromate  from  off  the 
filter  with  hydrochloric  acid.  Wash  well  and  de- 
termine the  chromic  acid  present  with  a  standard 
solution  of  ferrous  ammonium  sulphate,  using  a 
dilute  solution  of  potassium  ferricyanide  as  an 
outside  indicator.  The  ferrous  ammonium  sul- 
phate is  made  up  of  such  strength  that  1  c.c.  will 
equal  0.00202  gram  Fe.  For  a  one  gram  sample 
divide  the  number  of  c.c.  of  ferrous  ammonium 
sulphate  used  by  4. 

Details  of  this  calculation  are  given  under  the 
Analysis  of  Lead  Ores. 

Deduct  the  lead  found  as  lead  sulphate  from  the 
total  lead  and  calculate  the  residual  lead  to  PbO. 

Zinc1 

Boil  one  gram  of  the  sample  in  a  beaker  with 
the  following  solution: 

Water 30  c.c. 

Ammonium  chloride 4  grams. 

Concentrated    hydrochloric 
acid 6  c.c. 

iLow's  Technical  Methods  of  Ore  Analysis. 


12         Chemical  Analysis  of  Lead  and  Its  Compounds 

If  the  sample  is  not  quite  dissolved  the  result  is 
not  affected,  as  the  residue  is  lead  sulphate  or  pre- 
cipitated lead  chloride. 

Dilute  to  200  c.c.  with  hot  water,  add  2  c.c.  of 
a  saturated  sodium  thiosnlphate  solution  and  ti- 
trate with  a  standard  solution  of  potassium  fer- 
rocyanide,  spotting  out  on  a  5  per  cent  solution 
of  uranium  nitrate  as  outlined  under  the  Analysis 
of  Lead  Ores.  Calculate  the  zinc  to  zinc  oxide  by 
multiplying  by  the  factor  1.245. 

Iron  Oxide 

Determine  this  constituent  as  outlined  under  the 
Analysis  of  Litharge. 

U.  S.  Interdepartmental  Committee's  Recom- 
mended Specification  for  Basic  Sulphate 
White  Lead,  Dry  and  Paste1 

1.  General 

Basic  sulphate  white  lead  may  be  ordered  in  the 
form  of  dry  pigment  or  paste  ground  in  linseed 
oil.  Material  shall  be  purchased  by  net  weight. 

(a)  Dry  Pigment 

The  pigment  shall  be  the  sublimed  product  pre- 
pared from  lead  sulphide  ores,  free  from  impuri- 
ties and  adulterants,  and  shall  meet  the  following 
requirements : 

1Prepared  and  recommended  by  the  U.  S.  Interdepartmental  Committee  on 
Paint  Specification  Standardization,  September  22,  1919.  P.  H.  Walker, 
Bureau  of  Standards,  Chairman  ;  H.  E.  Smith,  U.  S.  Railroad  Administra- 
tion, Secretary.  Circular  of  the  Bureau  of  Standards.  No.  85. 


Sublimed  White  Lead  13 

Color — Color  strength :    When  specified  shall  be  equal  to  that  of 
a  sample  mutually  agreed  upon  by  buyer  and  seller. 

Coarse  particles1 :                                                                     Min.  Max. 

Eetained  on  standard  No.  200  screen None. 

Ketained  on  standard  No.  325  screen.  .  .per  cent 0.5 

Composition : 

Lead   oxide    do 11.0  18.0 

Zinc  oxide    do 9.0 

Total  impurities,  including  moisture do 1.0 

The  remainder  shall  be  lead  sulphate. 

,-f 

(b)  Pastes 

The  paste  shall  be  made  by  thoroughly  grind- 
ing the  dry  pigment  with  pure  raw  or  refined  lin- 
seed oil. 

The  paste  as  received  shall  not  be  caked  in  the 
container  and  shall  break  up  readily  in  oil  to  form 
a  smooth  paint  of  brushing  consistency.  It  shall 
mix  readily  in  all  proportions  without  curdling 
with  linseed  oil,  turpentine,  or  volatile  mineral 
spirits  or  any  combination  of  these  substances. 

The  paste  shall  consist  of : 

Min.  Max. 

Pigment    per  cent .  .        89  91.0 

Linseed  oil do 9  11.0 

Moisture  and  other  volatile  matter do 0.7 

Coarse  particles  and  "skins"  (total  residue  retained  on 

No.  325  screen,  based  on  pigment) per  cent.  .        .  .  0.5 

2.  Sampling 

It  is  mutually  agreed  by  buyer  and  seller  that  a 
single  package  out  of  each  lot  of  not  more  than 
1000  packages  be  taken  as  representative  of  the 
whole. 


irThe  No.  200  and  No.  325  screens  are  the  same  as  screens  formerly  known 
as  200  and  350  mesh. 


14        Chemical  Analysis  of  Lead  and  Its  Compounds 

With  the  dry  pigment,  this  package  shall  bo 
opened  by  the  inspector  and  a  sample  of  not  less 
than  5  pounds  taken  at  random  from  the  contents 
and  sent  to  the  laboratory  for  test. 

With  the  paste,  whenever  possible,  an  original 
unopened  container  shall  be  sent  to  the  laboratory; 
and  when  this  is  for  any  reason  not  done,  the  in- 
spector shall  determine,  by  thorough  testing  with 
a  paddle  or  spatula,  whether  the  material  meets 
the  requirement  regarding  not  caking  in  the  con- 
tainer. (See  4a.)  After  assuring  himself  that  the 
paste  is  not  caked  in  the  container  the  inspector 
shall  draw  a  sample  of  not  less  than  5  pounds  of 
the  thoroughly  mixed  paste,  place  it  in  a  clean  dry 
metal  or  glass  container,  which  must  be  filled  with 
the  sample,  closed  with  a  tight  cover,  sealed, 
marked,  and  sent  to  the  laboratory  for  test  with 
the  inspector's  report  on  caking  in  container. 

When  requested,  a  duplicate  sample  may  be 
taken  from  the  same  package  and  delivered  to  the 
seller,  and  the  inspector  may  take  a  third  sample 
to  hold  for  test  in  case  of  dispute. 

Samples  will  in  general  be  tested  by  the  follow- 
ing methods,  but  the  purchaser  reserves  the  right 
to  apply  any  additional  tests,  or  use  any  available 
information  to  ascertain  whether  the  material 
meets  the  specification. 

3.  Laboratory  Examination  of  Dry  Pigment 
(a)  Color 

Take  1  gram  of  the  sample,  add  10  to  12  drops 
linseed  oil,  rub  up  on  a  stone  slab  or  glass  plate 


Sublimed  White  Lead  15 

with  a  flat  bottomed  glass  or  stone  pestle  or  muller 
to  a  uniform  smooth  paste.  Treat  in  a  similar  man- 
ner, 1  gram  of  the  standard  basic  sulphate  white 
lead.  Spread  the  two  pastes  side  by  side  on  a  glass 
microscope  slide  and  compare  the  colors.  If  the 
sample  is  as  white  as  or  whiter  than  the  "stand- 
ard," it  passes  this  test.  If  the  "standard"  is 
whiter  than  the  sample,  the  material  does  not  meet 
the  specification. 

(b)  Color  Strength 

Weigh  accurately  0.01  gram  of  lampblack,  place 
on  a  large  glass  plate  or  stone  slab,  add  5  drops 
of  linseed  oil  and  rub  up  with  a  flat  bottomed  glass 
pestle  or  muller,  then  add  exactly  10  grams  of  the 
sample  and  45  drops  of  linseed  oil  and  grind  with 
a  circular  motion  of  the  muller  50  times;  gather 
up  with  a  sharp  edged  spatula  and  grind  out  twice 
more  in  a  like  manner,  giving  the  pestle  a  uniform 
pressure.  Treat  another  0.01  gram  of  the  same 
lampblack  in  the  same  manner  except  that  10  grams 
of  standard  basic  sulphate  white  lead  is  used  in- 
stead of  the  10  grams  of  the  sample.  Spread  the 
two  pastes  side  by  side  on  a  glass  microscope  slide 
and  compare  the  colors.  If  the  sample  is  as  light 
as  or  lighter  in  color  than  the  "standard,"  it 
passes  this  test.  If  the  "standard"  is  lighter  in 
color  than  the  sample,  the  material  does  not  meet 
the  specification. 

(c)  Coarse  Particles 

Dry  in  an  oven  at  105  to  110°  C.  a  No.  200  and 
a  No.  325  sieve,  cool,  and  weigh  accurately.  Weigh 


16         Chemical  Analysis  of  Lead  and  Its  Compounds 

100  grams  of  the  sample,  dry  at  100°  C. ;  transfer 
to  a  mortar,  add  100  c.c.  kerosene,  thoroughly  mix 
by  gentle  pressure  with  a  pestle  to  break  up  all 
lumps,  wash  with  kerosene  first  through  the  200 
and  then  through  the  325  sieve,  breaking  up  all 
lumps,  but  not  grinding.  After  washing  with  kero- 
sene until  all  but  the  particles  too  coarse  to  pass 
the  sieves  have  been  washed  through,  wash  all 
kerosene  from  the  sieves  with  ether  or  petroleum 
ether,  heat  the  sieves  for  one  hour  at  105  to  110° 
C.,  cool,  and  weigh.  The  increase  in  weight  of  the 
No.  200  sieve  should  be  not  more  than  0.010  gram, 
and  of  the  No.  325  sieve  not  more  than  0.500  gram. 

(d)  Qualitative  Analysis 

Test  for  matter  insoluble  in  acid  ammonium  ace- 
tate solution,  for  calcium,  for  carbonates,  and  for 
any  other  impurities  suspected  by  the  regular 
methods  of  qualitative  analysis. 

(e)  Moisture 

Place  one  gram  of  the  sample  in  a  tared,  wide 
mouth,  short  weighing  tube  provided  with  a  glass 
stopper.  Heat  with  stopper  removed  for  2  hours 
at  a  temperature  between  100  and  105°  C.  Insert 
stopper,  cool,  and  weigh.  Calculate  loss  in  weight 
as  moisture. 

(f)  Insoluble  Impurity  and  Total  Lead 

In  a  250-c.c.  beaker,  moisten  1  gram  of  the  pig- 
ment with  a  few  drops  of  alcohol ;  add  50  c.c.  of 
acid  ammonium  acetate  solution.  (See  reagents 
5a.)  Heat  to  boiling  and  boil  for  2  minutes.  De- 
cant through  a  filter  paper,  leaving  any  undecom- 


Sublimed  White  Lead  17 

posed  matter  in  the  beaker.  To  the  residue  in  the 
beaker,  add  50  c.c.  of  the  acid  ammonium  acetate 
solution,  heat  to  boiling,  and  boil  for  2  minutes. 
Filter  through  the  same  paper  and  wash  with  hot 
water.  If  an  appreciable  residue  remains,  ignite 
and  weigh  as  insoluble  impurity.  Unite  the  acid 
ammonium  acetate  solutions,  heat  to  boiling,  and 
add  dropwise,  with  stirring,  a  slight  excess  (in 
total  about  10  to  15  c.c.)  of  dichromate  solution. 
(See  reagents  55.)  Heat  until  the  precipitate 
assumes  an  orange  color,  let  settle,  filter  on  a 
weighed  Gooch  crucible,  wash  by  decantation  with 
hot  water  until  the  washings  are  colorless,  and 
finally  transfer  all  of  the  precipitate  to  the  cru- 
cible. Then  wash  with  10  c.c.  of  95  per  cent  ethyl 
alcohol  and  finally  with  10  c.c.  of  ethyl  ether.  Dry 
at  110  to  120°  C.,  cool,  and  weigh  PbCr04.  Calcu- 
late to  PbO  by  multiplying  by  the  factor  0.69. 

(g)  Zinc  Oxide 

Weigh  accurately  about  1  gram  of  the  pigment, 
transfer  to  a  400-c.c.  beaker,  add  30  c.c.  of  HC1 
(1 :2),  boil  for  2  or  3  minutes,  add  200  c.c.  of  water 
and  a  small  piece  of  litmus  p^per,  add  NH4OH 
until  slightly  alkaline,  render  just  acid  with  HC1, 
then  add  3  c.c.  of  concentrated  HC1,  heat  nearly 
to  boiling,  and  titrate  with  standard  potassium 
ferrocyanide  as  in  standardizing  that  solution. 
(See  reagents  5d.)  Calculate  total  zinc  as  ZnO. 

(h)  Lead  Sulphate 

Treat  0.5  gram  of  the  pigment  in  a  400-c.c.  beaker 
with  a  few  drops  of  alcohol,  add  10  c.c.  of  bromine 


18         Chemical  Analysis  of  Lead  and  Its  Compounds 

water,  10  c.c.  HC1  (1:1),  and  3  grams  of  NH4C1. 
Cover  with  a  watch  glass  and  heat  on  a  steam  bath 
for  5  minutes,  add  hot  water  to  give  a  total  vol- 
ume of  about  200  c.c.,  boil  for  5  minutes,  filter  to 
separate  any  insoluble  matter  (a  pure  pigment 
should  be  completely  dissolved),  and  wash  thor- 
oughly with  hot  water.  (The  insoluble  matter  may 
be  ignited,  weighed,  and  examined  qualitatively.) 
Neutralize  the  clear  solution  (original  solution  or 
filtrate  from  insoluble  matter)  in  a  covered  beaker 
with  dry  Na,CO.,,  add  1  gram  more  of  dry  Na2C03, 
and  boil  10  to  15  minutes.  Wash  off  cover,  let  set- 
tle, filter,  and  wash  with  hot  water.  Redissolve 
the  precipitate  in  HC1  (1:1),  reprecipitate  with 
Na^COs  as  above,  filter,  and  wash  thoroughly  with 
hot  water.  Acidify  the  united  filtrates  with  HC1, 
adding  about  1  c.c.  in  excess.  Boil  to  expel  bro- 
mine, and  to  the  clear  boiling  solution  add  slowly 
with  stirring  15  c.c.  of  barium  chloride  solution. 
(See  reagents  5e.)  Let  stand  on  steam  bath  for 
about  1  hour,  filter  on  a  weighed  Gooch  crucible, 
wash  thoroughly  with  boiling  water,  dry,  ignite, 
cool,  and  weigh  as  BaS04.  Calculate  to  PbSOt, 
using  the  factor  1.3. 

(i)  Calculations 

Calculate  the  percentage  of  PbSO4  to  PbO  by 
multiplying  by  the  factor  0.736  and  subtract  the 
result  from  the  percentage  of  PbO  found  under 
(/) ;  report  the  difference  as  PbO.  Report  ZnO 
found  under  (g)  as  percentage  of  ZnO.  Moisture 
and  insoluble  matter  are  reported  as  such. 


Sublimed  White  Lead  19 

4.  Laboratory  Examination  of  Paste 

(a)  Caking  in  Container 

When  an  original  package  is  received  in  the  lab- 
oratory it  shall  be  weighed,  opened,  and  stirred 
with  a  stiff  spatula  or  paddle.  The  paste  must  be 
no  more  difficult  to  break  up  and  show  no  more  cak- 
ing than  a  normal  good  grade  of  white  lead  paste. 
The  paste  shall  be  finally  thoroughly  mixed,  re- 
moved from  the  container,  and  the  container  wiped 
clean  and  weighed.  This  weight  subtracted  from 
the  weight  of  the  original  package  gives  the  net 
weight  of  the  contents.  A  portion  of  the  thor- 
oughly mixed  paste  shall  be  placed  in  a  clean  con- 
tainer and  the  portions  for  the  remaining  tests 
promptly  weighed  out  from  it. 

(b)  Mixing  with  Linseed  Oil 

One  hundred  grams  of  the  paste  shall  be  placed 
in  a  cup,  and  30  c.c.  of  linseed  oil  added  slowly  with 
careful  stirring  and  mixing  with  a  spatula  or  pad- 
dle. The  resulting  mixture  must  be  smooth  and  of 
good  brushing  consistency. 

(c)  Moisture  and  Other  Volatile  Matter 
Weigh  accurately  from  3  to  5  grams  of  the  paste 

into  a  tared  flat  bottomed  dish,  about  5  cm.  in  diam- 
eter, spreading  the  paste  over  the  bottom.  Heat 
at  105  to  110°  C.  for  1  hour,  cool,  and  weigh.  Cal- 
culate loss  in  weight  as  percentage  of  moisture 
and  other  volatile  matter. 

(d)  Percentage  of  Pigment 

Weigh  accurately  about  15  grams  of  the  paste 
into  a  weighed  centrifuge  tube.  Add  20  to  30  c.c. 


20         Chemical  Analysis  of  Lead  and  Its  Compounds 

of  "extraction  mixture"  (see  reagents),  mix  thor- 
oughly with  a  glass  rod,  wash  the  rod  with  more 
of  the  extraction  mixture,  and  add  sufficient  of  the 
reagent  to  make  a  total  of  60  c.c.  in  the  tube.  Place 
the  tube  in  the  container  of  a  centrifuge,  surround 
with  water,  and  counterbalance  the  container  of 
the  opposite  arm  with  a  similar  tube  or  a  tube  with 
water.  Whirl  at  a  moderate  speed  until  well  set- 
tled. Decant  the  clear  supernatant  liquid.  Repeat 
the  extraction  twice  with  40  c.c.  of  extraction  mix- 
ture and  once  with  40  c.c.  of  ether.  After  drawing 
off  the  ether,  set  the  tube  in  a  beaker  of  water  at 
about  80°  C.  or  on  top  of  a  warm  oven  for  10  min- 
utes, then  in  an  oven  at  110  to  115°  C.  for  2  hours. 
Cool,  weigh,  and  calculate  the  percentage  of  pig- 
ment. 

(e)  Examination  of  Pigment 

Grind  the  pigment  from  (d)  to  a  fine  powder, 
pass  through  a  No.  80  screen  to  remove  any 
"skins,"  preserve  in  a  stoppered  tube,  and  exam- 
ine as  under  3(o),  3(6),  3(d),  3(/),  3(#),  3(7i),  and 
3(t),  Laboratory  Examination  of  Dry  Pigment. 

(f)  Preparation  of  Fatty  Acids 

To  about  25  grains  of  the  paste  in  a  porcelain 
casserole,  add  15  c.c.  of  aqueous  sodium  hydroxide 
(see  reagents),  and  75  c.c.  of  ethyl  alcohol,  mix, 
and  heat  uncovered  on  a  steam  bath  until  saponi- 
fication  is  complete  (about  1  hour).  Add  100  c.c. 
of  water,  boil,  add  an  excess  of  sulphuric  acid  of 
specific  gravity  1.2  (8  to  10  c.c.  will  usually  suffice), 


Sublimed  White  Lead  21 

boil,  stir,  and  transfer  to  a  separatory  funnel  to 
which  some  water  has  been  previously  added. 
Draw  off  as  much  as  possible  of  the  acid  aqueous 
layer  and  PbS04  precipitate,  wash  once  with  water, 
then  add  50  c.c.  of  water  and  50  c.c.  of  ether.  Shake 
very  gently  with  a  whirling  motion  to  dissolve  the 
fatty  acids  in  the  ether,  but  not  violently,  so  as  to 
avoid  forming  an  emulsion.  Draw  off  the  aqueous 
layer  and  wash  the  ether  layer  with  one  15  c.c. 
portion  of  water  and  then  with  5  c.c.  portions  of 
water  until  free  from  sulphuric  acid.  Then  draw 
off  completely  the  water  layer.  Transfer  the  ether 
solution  to  a  dry  flask,  add  25  to  50  grams  of  anhy- 
drous sodium  sulphate.  Stopper  the  flask  and  let 
stand  with  occasional  shaking  at  a  temperature 
below  25°  C.  until  the  water  is  completely  removed 
from  the  ether  solution,  which  will  be  shown  by 
the  solution  becoming  perfectly  clear  above  the 
solid  sodium  sulphate.  Decant  this  clear  solution 
(if  necessary  through  a  dry  filter  paper)  into  a 
dry  100  c.c.  Erlenmeyer  flask.  Pass  a  rapid  cur- 
rent of  dry  air  (pass  through  a  CaCl2  tower)  into 
the  mouth  of  the  Erlenmeyer  flask  and  heat  to  a 
temperature  below  75°  C.  on  a  dry  hot  plate  until 
the  ether  is  entirely  driven  off.  The  fatty  acids 
prepared  as  above  should  be  kept  in  a  stoppered 
flask  and  examined  at  once.1 


xlt  is  important  to  follow  all  of  the  details  since  ether  generally  contains 
alcohol  and  after  washing  with  water  always  contains  water.  It  is  very 
difficult  to  remove  water  and  alcohol  by  evaporation  from  fatty  acids,  but 
the  washing  of  the  ether  solution  and  subsequent  drying  with  anhydrous 
sodium  sulphate  removes  both  water  and  alcohol.  Ether,  in  the  absence  of 
water  and  alcohol,  is  easily  removed  from  fatty  acids  by  gentle  heat. 


22         Chemical  Analysis  of  Lead  and  Its  Compounds 

(g)  Test  for  Mineral  Oil 

Place  10  drops  of  the  fatty  acid  (/)  in  a  50-c.c. 
test  tube,  add  5  c.c.  of  alcoholic  soda  (see  re- 
agents), boil  vigorously  for  5  minutes,  add  40  c.c. 
of  water,  and  mix ;  a  clear  solution  indicates  that 
not  more  than  traces  of  unsaponifiable  matter  are 
present.  If  the  solution  is  not  clear  the  oil  is  not 
pure  linseed  oil. 

(h).  Iodine  Number  of  Fatty  Acids 

Place  a  small  quantity  of  the  fatty  acids  (/)  in 
a  small  weighing  burette  or  beaker  and  weigh  ac- 
curately. Transfer  by  dropping  about  0.15  gram 
(0.10  to  0.20  gram)  to  a  500-c.c.  bottle  having  a 
well  ground  glass  stopper,  or  an  Erlenmeyer  flask 
having  a  specially  flanged  neck  for  the  iodine  test, 
lieweigh  the  burette  or  beaker  and  determine  the 
amount  of  sample  used.  Add  10  c.c.  of  chloroform 
and  whirl  the  bottle  to  dissolve  the  sample.  Add 
10  c.c.  of  chloroform  to  each  of  two  empty  bottles 
like  that  used  for  the  sample.  Add  to  each  bottle 
25  c.c.  of  the  Hanus  solution  (see  reagents  5&) 
and  let  stand  with  occasional  shaking  for  one-half 
hour.  Add  10  c.c.  of  the  15  per  cent  potassium 
iodide  solution  and  100  c.c.  of  water,  and  titrate 
with  standard  sodium  thiosulphate,  using  starch 
as  indicator.  The  titration  on  the  two  blank  tests 
should  agree  within  0.1  c.c.  From  the  difference 
between  the  average  of  the  blank  titrations  and 
the  titration  on  the  sample  and  the  iodine  value 
of  the  thiosulphate  solution,  calculate  the  iodine 
number  of  the  sample  tested.  (Iodine  number  is 


Sublimed  White  Lead  23 

centigrams  of  iodine  to  1  gram  of  sample.)  If  the 
iodine  number  is  less  than  170,  the  oil  does  not 
meet  the  specification. 

(i)  Coarse  Particles  and  "Skins" 

Weigh  out  an  amount  of  paste  containing  100 
grams  of  pigment  (see  d),  add  100  c.c.  of  kerosene, 
wash  through  No.  325  screen,  and  weigh  the  resi- 
due as  in  3  (c).  The  total  residue  left  on  the  screen 
should  be  not  more  than  0.5  gram. 

5.  Reagents 

(a)  Acid  Ammonium  Acetate  Solution 

Mix  150  c.c.  of  80  per  cent  acetic  acid,  100  c.c. 
of  water,  and  95  c.c.  of  strong  ammonia  (specific 
gravity  0.90). 

(b)  Bichromate  Solution 

Dissolve  100  grams  sodium  dichromate  (Na2 
Cr207.2H20)  or  potassium  dichromate  (K2Cr207) 
in  water  and  dilute  to  1000  c.c. 

(c)  Uranyl  Indicator  for  Zinc  Titration 

A  5  per  cent  solution  of  uranyl  nitrate  in  water 
or  a  5  per  cent  solution  of  uranyl  acetate  in  water 
made  slightly  acid  with  acetic  acid. 

(d)  Standard  Potassium  Ferrocyanide 
Dissolve  22  grams  of  the  pure  salt  in  water  and 

dilute  to  1000  c.c.  To  standardize,  transfer  about 
0.2  gram  (accurately  weighed)  of  pure  metallic 
zinc  or  freshly  ignited  pure  ZnO  to  a  400-c.c. 
beaker.  Dissolve  in  10  c.c.  of  HC1  and  20  c.c.  of 


24        Chemical  Analysis  oj  Lead  and  Its  Compounds 

water.  Drop  in  a  small  piece  of  litmus  paper,  add 
NH4OH  until  slightly  alkaline,  then  add  HC1  until 
just  acid  and  finally  add  3  c.c.  of  strong  HC1.  Di- 
lute to  about  250  c.c.  with  hot  water  and  heat  nearly 
to  boiling.  Run  in  the  ferrocyanide  solution 
slowly  from  a  burette  with  constant  stirring  until 
a  drop  tested  on  a  white  porcelain  plate  with  a 
drop  of  the  uranyl  indicator  shows  a  brown  tinge 
after  standing  1  minute.  A  blank  should  be  run 
with  the  same  amounts  of  reagents  and  water  as 
in  the  standardization.  The  amount  of  ferro- 
cyanide solution  required  for  the  blank  should  be 
subtracted  from  the  amounts  used  in  standardiza- 
tion and  in  titration  of  the  sample.  The  standard- 
ization must  be  made  under  the  same  conditions  of 
temperature,  volume,  and  acidity  as  obtain  when 
the  sample  is  titrated. 

(e)  Barium  Chloride  Solution 

Dissolve  100  grams  of  pure  crystallized  barium 
chloride  in  water  and  dilute  to  1000  c.c. 

(f)  Standard  Sodium  Thiosulphate  Solution 
Dissolve  pure  sodium  thiosulphate  in  distilled 

water  that  has  been  well  boiled  to  free  it  from  CO2 
in  the  proportion  of  24.83  grams  of  crystallized 
sodium  thiosulphate  to  1000  c.c.  of  the  solution. 
It  is  best  to  let  this  solution  stand  for  about  two 
weeks  before  standardizing.  Standardize  with 
pure  resublimed  iodine.  (See  Treadwell-Hall, 
Analytical  Chemistry,  vol.  II,  3d  ed.,  p.  646.)  This 
solution  will  be  approximately  decinormal,  and  it 
is  best  to  leave  it  as  it  is  after  determining  its  exact 


Sublimed  White  Lead  25 

iodine  value,  rather  than  to  attempt  to  adjust  it 
to  exactly  decinormal  strength.  Preserve  in  a 
stock  bottle  provided  with  a  guard  tube  filled  with 
soda  lime. 

(g)  Starch  Solution 

Stir  up  2  to  3  grams  of  potato  starch  or  5  grams 
of  soluble  starch  with  100  c.c.  of  1  per  cent  sali- 
cylic acid  solution,  add  300  to  400  c.c.  of  boiling 
water,  and  boil  the  mixture  until  the  starch  is  prac- 
tically dissolved ;  then  dilute  to  1  liter. 

(h)  Extraction  Mixture 

Mix  10  volumes  ether  (ethyl  ether),  6  volumes 
benzol,  4  volumes  methyl  alcohol,  and  1  volume 
acetone. 

(i)  Aqueous  Sodium  Hydroxide 

Dissolve  100  grams  of  NaOH  in  distilled  water 
and  dilute  to  300  c.c. 

(j)  Potassium  Iodide  Solution 

Dissolve  150  grams  of  potassium  iodide  free 
from  iodate  in  distilled  water  and  dilute  to 
1000  c.c. 

( k)  Hanus  Solution 

Dissolve  13.2  grams  of  iodine  in  1000  c.c.  of  gla- 
cial acetic  acid,  99.5  per  cent,  which  will  not  reduce 
chromic  acid.  Add  enough  bromine  to  double  the 
halogen  content,  determined  by  titration  (3  c.c.  of 
bromine  is  about  the  proper  amount).  The  iodine 
may  be  dissolved  by  the  aid  of  heat,  but  the  solu- 
tion should  be  cold  when  the  bromine  is  added. 


26        Chemical  Analysis  of  Lead  and  Its  Compounds 

(1)  Alcoholic  Sodium  Hydroxide  Solution 

Dissolve  pure  sodium  hydroxide  in  95  per  cent 
ethyl  alcohol  in  the  proportion  of  about  22  grams 
per  1000  c.c.  Let  stand  in  a  stoppered  bottle.  De- 
cant the  clear  liquid  into  another  bottle,  and  keep 
well  stoppered.  This  solution  should  be  colorless 
or  only  slightly  yellow  when  used;  it  will  keep 
colorless  longer  if  the  alcohol  is  previously  treated 
with  NaOH  (about  80  grams  to  1000  c.c.)  kept  at 
about  50°  C.  for  15  days,  and  then  distilled. 


CHAPTER    III 

THE  LEAD  CONTENTS  IN  SUBLIMED 
WHITE  LEAD— A  CALCULATION1 

The  composition  of  sublimed  white  lead,  the  basic 
sulphate  of  lead,  has  become  a  most  important  fac- 
tor to  users  of  this  pigment.  Both  among  rubber 
manufacturers  and  producers  of  paints,  it  is  being- 
found  essential  that  the  contents  of  lead  oxide  and 
lead  sulphate  be  known,  so  that  advantage  may  be 
fully  taken  of  its  characteristic  properties.  This 
control  necessitates  an  analysis  of  the  compound 
in  the  laboratory. 

In  analyzing  sublimed  white  lead  by  the  usual 
method,  it  is  found  that  the  percentage  composition 
can  be  determined  only  by  an  analysis  entailing 
lengthy  manipulation,  in  which  the  content  of  lead 
oxide  is  directly  dependent  upon  the  accuracy  of 
the  other  determinations,  owing  to  the  necessity 
of  estimating  its  percentage  by  a  calculation  based 
upon  the  percentage  of  the  other  constituents 
present.  The  steps  in  the  procedure  must  therefore 
be  closely  watched  for  slight  inaccuracies  at  all 
times. 

As  is  well  known,  the  average  composition  of 
sublimed  white  lead  is  given  as  follows  : 

Lead  sulphate 78.5 

Lead  oxide 16.0 

Zinc  oxide 5.5 

ij.  Ind.  &  Eng.  Chem.,  6,  200  (1914). 

27 


28         Chemical  Analysis  of  Lead  and  Its  Compounds 

That  its  composition  varies  only  slightly  from 
the  above  analysis  during  a  long  period  of  time, 
is  shown  by  its  comparison  with  an  average  of  the 
entire  output  of  the  Eagle-Picher  Lead  Company 
extending  over  five  months'  time,  an  average  em- 
bracing 270  total  analyses. 

This  average  shows  the  composition  to  be : 

Lead  sulphate 76.68 

Lead  oxide 17.23 

Zinc  oxide 5.79 

99.70 

A  slightly  higher  lead  oxide  and  zinc  oxide 
content  and  a  correspondingly  lower  lead  sulphate 
content  is  found,  than  in  the  usually  stated  formula. 
It  shows,  however,  only  slight  variation.  The  aver- 
age total  percentage,  consisting  of  lead  sulphate, 
lead  oxide,  and  zinc  oxide,  was  found  to  be  99.70 
per  cent.  The  remaining  0.3  of  a  per  cent  is  only 
rarely  determined,  and  when  actually  sought  is 
found  to  consist  of  moisture,  occluded  gas  and  ash. 
A  definite  ratio  exists  between  the  total  lead  con- 
tent and  the  lead  sulphate  and  lead  oxide  contents, 
and  advantage  may  be  taken  of  this  relation  for  a 
rapid  and  accurate  determination  of  the  lead  con- 
stituents in  sublimed  white  lead. 

In  order  to  arrive  at  the  short  method  for  the 
analysis  which  is  based  upon  a  direct  calculation  of 
the  lead  and  zinc  contents,  it  is  necessary  that  only 
the  percentage  of  zinc  and  lead  be  determined  by 
the  methods  already  described. 


The  Lead  Contents  in  Sublimed  White  Lead  29 

Using  the  percentages  of  zinc  oxide  and  total 
lead,  together  with  the  average  total,  99.70  per 
cent,  determined  from  the  large  number  of  analy- 
ses, the  contents  of  lead  oxide  and  lead  sulphate 
are  readily  estimated  by  the  following  calculation : 

Total  percentage  of  lead  compounds  present  equals  99.70  per  cent  (average) 
=  total  percentage  found  of  ZnO,  PbO  and  PbSO4  less  percentage  ZnO. 
Total  percentage  of  lead  compounds  present  equals  99.70  per  cent    (average 
total)   minus  percentage  ZnO. 

Atomic  weight  lead 207.1 

Molecular  weight  lead  oxide 223.1 

Molecular  weight  lead  sulphate 303.1 

As  a  hypothetical  case,  we  can  assume  the  presence  of  a  4.70  per  cent 
ZnO  and  69.00  per  cent  metallic  lead. 

(Mol.  wt.   PbS04  \ 
X    %   Pb  found  I   —  %   Pb  constituents 
At.  wt.  Pb.  / 

=   %    PbO  present 

Mol.  wt.  PbSO4  —  mol.  wt.  PbO 


Mol.  wt.  PbO 

/Mol.  wt. 

(2) 


(Mol.  wt.  PbO  \ 
X    %  Pb  found       I   —  %   Pb  constituents 
At.   wt.  Pb  / 


Mol.  wt.  PbO  — Mol.  wt.  PbS04 


=   %  PbSO4  present 


Mol.  wt.  PbSO4 
Determining  the  percentage  of  lead  oxide  and  lead  sulphate  present  by 

aVir\\70    f r\fw n  1  a e    -wro    finrl  • 


the  above  formulas  we  find : 

/303.1  \ 

(1)      | X    69.00  I    —  95.00 

—  per  cent  PbO  ~  16.68 


(303.1  \ 
X    69.00  I    —  95. ( 
207.1  / 


303.1   —  223.1 
223.1 


(223.1  \ 
X    69.00  I    —  95.' 
207.1  / 


(2)      I  X    69.00  I    —  95.00 

=  per  cent  PbSO4  -  78.32 

J.I  —  303.1 


303.1 

Therefore  by  substituting  the  percentages  of 
lead  and  zinc  oxide  in  the  following  formula  which 
is  derived  from  equation  (1)  the  percentage  of 
PbO  in  the  sublimed  white  lead  is  easily  found. 


30        Chemical  Analysis  of  Lead  and  Its  Compounds 

The  sum  of  the  percentages  of  zinc  oxide  and  lead 
oxide  subtracted  from  99.7  gives  the  percentage 
of  lead  sulphate. 

Per  cent  PbO  =  [1.464  X  %  Pb  —  (99.7  —  %  ZnO)]  2.79. 

A  comparison  of  the  actual  results  obtained  by 
the  complete  analysis  of  sublimed  white  lead  and 
its  calculated  composition  shows  that  the  values 
obtained  are  concordant.  Indeed  the  only  essential 
factors  for  the  short  method  are  accurate  deter- 
minations of  the  lead  and  zinc  contents.  The  re- 
moval of  several  steps  in  the  analysis  leads  to 
greater  accuracy  coupled  with  a  considerable  cur- 
tailment of  time. 

A  table  of  comparisons  shows  the  following  con- 
cordance of  results: 

Lead          Lead         Zinc          Total 
No.         Analysis  sulphate      oxide        oxide          lead         Total 

1  Complete 79.20  15.28  5.23         68.30         99.72 

Calculated   79.17  15.30  

2  Complete   77.74  16.81  5.11         68.70         99.66 

Calculated   77.97  16.62 

3  Complete   77.09  16.95  5.73         68.40         99.77 

Calculated   76.85  17.12  

4  Complete 80.20  14.66  4.86         68.40         99.72 

Calculated   80.15  14.69  

5  Complete   78.00  16.60  5.11         68.70         99.71 

Calculated   77.97  16.62  

6  Complete   77.84  17.10  4.86         69.00         99.80 

Calculated   77.69  17.15  

7  Complete   77.22  16.20  6.23         67.80         99.63 

Calculated     77.41  16.06  

8  Complete   74.10  20.21  5.48         69.40         99.79 

Calculated   74.00  20.22  

9  Complete    77.63  15.92  6.23         67.80         99.78 

Calculated  77.41  16.06  

10  Complete   76.05  17.93  5.73         68.60         99.71 

Calculated 76.04  17.93  

11  Complete   76.98  17.78  4.98         69.10         99.74 

Calculated   ..  ..  76.85  17.87  


The  Lead  Contents  in  Sublimed  White  Lead          31 

That  this  method  will  prove  of  value  will  be 
readily  appreciated  by  all  chemists  who  have  to 
determine  the  percentage  composition  of  any  basic 
sulphate  of  lead,  either  for  the  purpose  of  meeting 
specifications  or  for  accurate  control  of  finished 
products. 


CHAPTEE    IV 

SUBLIMED  BLUE  LEAD 

Sublimed  blue  lead  is  at  the  present  time  find- 
ing its  greatest  value  as  an  inhibitive  pigment  for 
the  protection  of  iron  and  steel.  The  high  rating 
given  to  this  pigment  on  exposure  tests  conducted 
under  the  supervision  of  the  American  Society 
for  Testing  Materials  for  the  prevention  of  cor- 
rosion is  bringing  it  more  and  more  to  the  at- 
tention of  paint  technologists  and  engineers. 

In  composition  it  consists  of  lead  sulphate,  lead 
sulphide,  lead  sulphite,  lead  oxide  and  zinc  oxide, 
with  occasional  traces  of  carbon.  Its  color  is  a 
pleasing  dull  steel  gray. 

Analysis 

Total  Lead 

The  total  lead  content  is  determined  volumetri- 
cally  as  outlined  under  the  estimation  of  Lead  in 
Lead  Ores. 

Total  Sulphur 

Treat  one-half  gram  of  the  sample  in  a  beaker 
with  10  c.c.  of  water  and  a  few  c.c.  of  bromine 
water.  Boil  gently  until  all  the  bromine  has  passed 
off.  Dilute  with  water,  add  another  portion  of 
bromine  water,  boil  and  continue  the  treatment 
until  the  sediment  has  become  white  in  color.  Add 

32 


Sublimed  Blue  Lead  33 

8  c.c.  of  nitric  acid,  evaporate  the  solution  until 
the  brown  fumes  of  nitric  acid  have  disappeared, 
dilute  with  water  and  add  an  excess  of  sodium  car- 
bonate. From  this  point  proceed  with  the  deter- 
mination of  the  sulphate  as  outlined  under  Sub- 
limed White  Lead. 

Lead  Sulphate 

On  a  separate  sample  determine  the  lead  sul- 
phate as  outlined  under  Sublimed  White  Lead,  by 
transposition  of  the  sulphate  with  sodium  car- 
bonate. 

Lead  Sulphite 

Boil  one  and  one-half  grams  of  the  sample  with 
3  grams  of  sodium  carbonate,  allow  to  stand,  fil- 
ter and  thoroughly  wash.  To  the  filtrate  add  3 
c.c.  of  bromine  water,  heat  gently  to  oxidize  the 
sodium  sulphite  to  sulphate,  acidify  with  HC1  and 
precipitate  the  sulphate  with  barium  chloride.  Fil- 
ter, wash  and  weigh  in  the  usual  manner.  The 
barium  sulphate  formed  will  contain  both  the  sul- 
phur present  as  sulphate  and  that  present  as  sul- 
phite converted  to  sulphate.  Deduct  the  amount 
present  as  sulphate  and  calculate  the  remainder  to 
lead  sulphite. 

Lead  Sulphide 

Deduct  the  sulphur  present  as  sulphate  and  sul- 
phite from  the  total  sulphur  and  report  the  dif- 
ference as  lead  sulphide. 


34        Chemical  Analysis  of  Lead  and  Its  Compounds 

Lead  Carbonate 

A  small  amount  of  lead  may  be  present  as  car- 
bonate. Determine  the  carbonic  acid  present  as 
outlined  under  Basic  Carbonate  White  Lead,  and 
calculate  this  carbonic  acid  to  lead  carbonate. 

Lead  Oxide 

Deduct  the  lead  present  as  lead  sulphate,  lead 
sulphite,  lead  sulphide  and  lead  carbonate  from 
the  total  lead  and  report  the  difference  as  lead 
oxide. 

Zinc  Oxide 

Determine  the  zinc  present  as  outlined  under 
Sublimed  White  Lead,  and  report  it  as  zinc  oxide. 

Carbon  and  Volatile  Matter 

Ignite  the  sample  in  a  partially  covered  cruci- 
ble at  a  low  heat  for  two  hours.  Report  the  dif- 
ference as  carbon  and  volatile  matter. 


CHAPTER    V 

ZINC  OXIDE 

Zinc  oxides  are  usually  analyzed  for  zinc  oxide, 
lead  sulphate  and  water  soluble.  In  addition  to 
this  certain  physical  properties  are  often  examined 
and  these  tests  often  are  as  important  as  the  chem- 
ical analysis.  The  usual  physical  tests  made  on 
pigments  are  found  on  page  148. 

Analysis 

Zinc  Oxide 

When  high  grade  oxides  containing  more  than 
99%  pure  ZnO  are  to  be  analyzed  it  is  best  to  obtain 
total  impurities  and  report  the  ZnO  by  difference. 
Ordinarily,  however,  the  zinc  content  should  be 
determined  as  described  on  page  39. 

Lead  Sulphate 

For  leaded  zincs  having  more  than  20  per  cent 
lead  the  method  described  for  Sublimed  White 
Lead,  on  page  10,  should  be  used.  For  all  others 
weigh  up  a  one  gram  sample  and  proceed  by  the 
Bichromate  Method  as  described  on  page  10.  The 
percentage  lead  times  1.464  equals  percentage  lead 
sulphate. 

35 


36         Chemical  Analysis  of  Lead  and  Its  Compounds 

Water  Soluble 

Since  the  water  soluble  material  in  zinc  oxide  is 
practically  all  zinc  sulphate  the  following  method 
has  been  found  quite  accurate  and  considerably 
shorter  than  the  methods  usually  employed. 

Weigh  up  5  grams  of  the  sample  and  pour  it  into 
a  beaker  containing  200  c.c.  boiling  hot  water.  Stir 
the  suspension  vigorously  for  one  minute  without 
further  boiling  and  allow  the  zinc  oxide  to  settle. 
Filter  the  supernatant  liquor  into  a  clean  beaker 
taking  great  care  not  to  allow  any  of  the  milky 
liquor  to  spatter  into  the  beaker  with  the  filtrate. 
Wash  the  zinc  oxide  onto  the  filter  paper  with  hot 
water,  wash  twice  and  allow  to  drain. 

To  the  filtrate  add  5  grams  ammonium  chloride, 
6  c.c.  concentrated  hydrochloric  acid  and  heat  to 
boiling.  Titrate  hot  with  standard  potassium 
ferrocyanide  solution  using  ammonium  molybdate 
as  outside  indicator.  A  blank  should  be  run  with 
200  c.c.  water,  5  grams  ammonium  chloride  and  G 
c.c.  concentrated  hydrochloric  acid  and  this  amount 
subtracted  from  values  obtained  with  zinc  oxide. 

The  factor  converting  zinc  to  zinc  sulphate  is 
2.47. 

Total  Sulphur 

Total  sulphur  may  be  determined  by  the  method 
described  on  page  40.  A  10  gram  sample  should 
be  used. 


Zinc  Oxide  37 

U.  S.  Interdepartmental  Committee's  Recom- 
mended Laboratory  Examination  for 
Zinc  Oxide,  Dry  and  Paste1 

1.     Laboratory  Examination,  Dry  Pigment 

(a)  Color 

Take  5  grams  of  the  sample,  add  1.5  c.c.  of  lin- 
seed oil,  rub  up  on  a  stone  slab  or  glass  plate  with 
a  flat  bottomed  glass  or  stone  pestle  or  muller  to  a 
uniform  smooth  paste.  Treat  in  a  similar  manner 
5  grams  of  the  standard  zinc  oxide.  Spread  the 
two  pastes  side  by  side  on  a  clear  colorless  glass 
plate  and  compare  the  colors.  If  the  sample  is  as 
white  as  or  whiter  than  the  "standard,"  it  passes 
this  test.  If  the  "standard"  is  whiter  than  the 
sample,  the  material  does  not  meet  the  specifica- 
tion. 

(b)  Color  Strength 

Weight  accurately  0.01  gram  of  lampblack,  place 
on  a  large  glass  plate  or  stone  slab,  add  0.2  c.c. 
of  linseed  oil  and  rub  up  with  a  flat  bottomed  glass 
pestle  or  muller,  then  add  exactly  10  grams  of  the 
sample  and  2.5  c.c.  of  linseed  oil,  and  grind  with 
a  circular  motion  of  the  muller  50  times ;  gather 
up  with  a  sharp  edged  spatula  and  grind  out  twice 
more  in  a  like  manner,  giving  the  pestle  a  uniform 
pressure.  Treat  another  0.01  gram  of  the  same 
lampblack  in  the  same  manner  except  that  10 

Prepared  and  recommended  by  the  U.  S.  Interdepartmental  Committee  on 
Paint  Specification  Standardization,  January  12,  1920.  P.  H.  Walker, 
Bureau  of  Standards,  Chairman  ;  H.  E.  Smith,  U.  S.  Railroad  Administra- 
tion, Secretary.  Circular  of  the  Bureau  of  Standards.  No.  87. 


38         Chemical  Analysis  of  Lead  and  Its  Compounds 

grams  of  standard  zinc  oxide  is  used  instead  of 
the  10  grams  of  the  sample.  Spread  the  two  pastes 
side  by  side  on  a  glass  microscope  slide  and  com- 
pare the  colors.  If  the  sample  is  as  light  as  or 
lighter  in  color  than  the  "  standard, "  it  passes  this 
test.  If  the  "  standard "  is  lighter  in  color  than 
the  sample,  the  material  does  not  meet  the  speci- 
fication. 

(c)  Coarse  Particles 

Dry  in  an  oven  at  105  to  110°  C.  a  standard  No. 
200  brass  or  copper  sieve,  cool  and  weigh  accu- 
rately. Weigh  50  grams  of  pigment  which  has 
been  previously  thoroughly  dried  by  heating  in  an 
oven  at  105  to  110°  C.  until  all  moisture  is  driven 
off.  Transfer  to  a  wide  mouth  bottle  or  cylinder 
of  about  300  c.c.  capacity,  add  about  200  c.c.  of 
dry  kerosene,  stopper  and  shake  vigorously  for 
about  5  minutes.  Remove  stopper  and  wash  back 
into  the  cylinder  with  a  jet  of  kerosene  any  pig- 
ment adhering  to  the  stopper.  Pour  about  50  c.c. 
of  the  kerosene  with  suspended  pigment  onto  the 
sieve,  let  drain  through  and  gradually  transfer  the 
whole  of  the  kerosene  and  pigment  to  sieve,  finally 
using  a  jet  of  kerosene  to  transfer  the  last  of  the 
pigment.  With  proper  manipulation  a  large  por- 
tion of  the  pigment  will  pass  through  the  sieve 
during  the  process  of  transferring  from  the  cylin- 
der. When  all  pigment  has  been  thrown  on  the 
sieve,  wash  with  a  jet  of  kerosene  until  no  more 
pigment  passes  through.  To  make  sure  that  all 
particles  have  been  thoroughly  washed  through, 


Zinc  Oxide  39 

move  the  sieve  from  over  the  vessel  in  which  the 
main  portion  of  kerosene  and  pigment  have  been 
caught  to  over  a  clear  glass  dish  resting  on  a  black 
surface  and  wash  all  portions  of  the  sieve  with  a 
jet  of  kerosene,  using  not  less  than  200  c.c.  of  kero- 
sene. This  kerosene  caught  in  this  dish  should 
be  entirely  free  from  pigment.  If  any  pigment 
can  be  seen  in  the  liquid,  repeat  washing  until  at 
least  200  c.c.  can  be  washed  through  without  show- 
ing any  pigment.  Then  wash  with  a  jet  of  kerosene 
all  pigment  adhering  to  the  frame  of  the  sieve 
beneath  the  wire  mesh.  Finally  wash  the  kerosene 
from  the  sieve  with  petroleum  ether,  dry  at  105 
to  110°,  cool  and  weigh.  The  increase  in  weight 
should  be  not  more  than  0.01  gram. 

+ 

(d)  Qualitative  Analysis 

Test  for  matter  insoluble  in  hydrochloric  acid, 
for  lead,  calcium,  etc.,  by  regular  methods  of  quali- 
tative analysis. 

(e)  Zinc  Oxide 

With  samples  free  from  impurities  (see  (d)), 
ignite  a  weighed  sample  and  calculate  the  residue 
as  ZnO.  With  samples  containing  impurity,  pro- 
ceed as  follows :  Weigh  accurately  about  0.25 
gram,  transfer  to  a  400-c.c.  beaker,  moisten  with 
alcohol,  dissolve  in  10  c.c.  of  hydrochloric  acid 
and  20  c.c.  of  water  and  titrate  with  standard 
potassium  ferrocyanide  following  the  procedure 
used  in  standardizing  this  reagent.  (See  3(i).) 


40        Chemical  Analysis  of  Lead  and  Its  Compounds 

(f)  Total  Sulphur 

Weigh  accurately  about  10  grams  of  the  sample. 
Moisten  with  a  few  drops  of  alcohol,  add  5  c.c.  of 
bromine  water  (saturated  solution  of  bromine), 
then  concentrated  hydrochloric  acid  in  excess,  boil 
to  expel  bromine,  and  dilute  to  about  100  c.c.  (Ma- 
terial complying  with  the  specification  should  all 
go  into  solution ;  if  insoluble  matter  remains,  filter 
and  examine  by  appropriate  methods.)  Make  alka- 
line with  ammonia,  then  just  acid  with  hydrochlo- 
ric acid,  heat  to  boiling  and  add  about  10  c.c.  of 
hot  barium  chloride  solution.  (See  reagents.) 
Let  stand  several  hours  (overnight),  filter  on  a 
weighed  Gooch  crucible,  wash  thoroughly  with  hot 
water,  dry,  ignite,  cool,  and  weigh  the  BaSO4.  Cal- 
culate to' 8  (BaSK)4  X  0.1373  ==  8). 

2.     Laboratory  Examination,  Paste 
(a)   CaJch/f/   in   Container 

When  an  original  package  is  received  in  the  lab- 
oratory, it  shall  be  weighed,  opened,  and  stirred 
with  a  stiff  spatula  or  paddle.  The  paste  must  be 
no  more  difficult  to  break  up  and  show  no  more 
caking  than  a  normal  good  grade  of  zinc  oxide 
paste.  The  paste  shall  be  finally  thoroughly 
mixed,  removed  from  the  container,  the  container 
wiped  clean,  and  weighed.  This  weight  subtracted 
from  the  weight  of  the  original  package  gives  the 
net  weight  of  the  contents.  A  portion  of  the  thor- 
oughly mixed  paste  shall  be  placed  in  a  clean  con- 
tainer and  the  portions  for  the  remaining  tests 
promptly  weighed  out. 


Zinc  Oxide  41 

(b)  Mixing  with  Linseed  Oil 

One  hundred  grams  of  the  paste  shall  be  placed 
in  a  cup,  35  c.c.  of  linseed  oil  added  slowly  with 
careful  stirring  and  mixing  with  a  spatula  or  pad- 
dle. The  resulting  mixture  must  be  smooth  and 
of  good  brushing  consistency. 

(c)  Moisture  and  Other  Volatile  Matter 

Weigh  accurately  from  3  to  5  grams  of  the  paste 
into  a  tared  flat  bottomed  dish,  about  5  cm.  in 
diameter,  spreading  the  paste  over  the  bottom. 
Heat  at  105  to  110°  C.  for  one  hour,  cool,  and  weigh, 
Calculate  loss  in  weight  as  percentage  moisture 
and  other  volatile  matter. 

(d)  Per  Cent  Pigment 

Weigh  accurately  about  15  grams  of  the  paste 
into  a  weighed  centrifuge  tube.  Add  20  to  30  c.c. 
of  " extraction  mixture "  (see  reagents),  mix  thor- 
oughly with  a  glass  rod,  wash  the  rod  with  more 
of  the  extraction  mixture,  and  add  sufficient  of  the 
reagent  to  make  a  total  of  60  c.c.  in  the  tube.  Place 
the  tube  in  the  container  of  a  centrifuge,  surround 
with  water,  and  counterbalance  the  container  of 
the  opposite  arm  with  a  similar  tube  or  a  tube  with 
water.  Whirl  at  a  moderate  speed  until  clear.  De- 
cant the  clear  supernatant  liquid.  Repeat  the 
extraction  twice  with  40  c.c.  portions  of  extraction 
mixture,  and  once  with  40  c.c.  of  ether.  After 
drawing  off  the  ether,  set  the  tube  in  a  beaker  of 
water  at  about  80°  C.  or  on  top  of  a  warm  oven 
for  10  minutes,  then  in  an  oven  at  110  to  115°  C. 


42        Chemical  Analysis  of  Lead  and  Its  Compounds 

for  2  hours.    Cool,  weigh,  and  calculate  percentage 
of  pigment. 

(e)  Examination  of  Pigment 

Grind  the  pigment  from  (d)  to  a  fine  powder, 
pass  through  a  No.  80  sieve  to  remove  any  ' '  skins, ' ' 
preserve  in  a  stoppered  tube  and  apply  tests  1  (d), 
(e),  and  (/).  If  required,  apply  tests  1  (a)  and 
(b)  in  comparison  with  a  portion  of  pigment  ex- 
tracted from  the  standard  paste  in  exactly  the 
same  manner  as  in  extracting  the  sample. 

(f)  Preparation  of  Fatty  Acids 

To  about  25  grams  of  the  paste  in  a  porcelain 
casserole  add  15  c.c.  aqueous  sodium  hydroxide 
(see  reagents),  and  75  c.c.  of  ethyl  alcohol,  mix 
and  heat  uncovered  on  a  steam  bath  until  saponi- 
fication  is  complete  (about  one  hour).  Add  100 
c.c.  water,  boil,  add  an  excess  of  sulphuric  acid  of 
specific  gravity  1.2  (8  to  10  c.c.  will  usually  suffice), 
boil,  stir,  and  transfer  to  a  separatory  funnel  to 
which  some  water  has  been  previously  added. 
Draw  off  as  much  as  possible  of  the  acid  aqueous 
layer,  wash  once  with  water;  then  add  50  c.c.  of 
water  and  50  c.c.  of  ether.  Shake  very  gently  with 
a  whirling  motion  to  dissolve  the  fatty  acids  in  the 
ether,  but  not  violently,  so  as  to  avoid  forming  an 
emulsion.  Draw  off  the  aqueous  layer  and  wash  the 
ether  layer  with  one  15  c.c.  portion  of  water  and 
then  with  5  c.c.  portions  of  water  until  free  from 
sulphuric  acid.  Then  draw  off  completely  the  water 
layer.  Transfer  the  ether  solution  to  a  dry  flask, 


Zinc  Oxide  43 

and  add  25  to  50  grams  of  anhydrous  sodium  sul- 
phate. Stopper  the  flask  and  let  stand  with  occa- 
sional shaking  at  a  temperature  below  25°  C.  until 
the  water  is  completely  removed  from  the  ether 
solution,  which  will  be  shown  by  the  solution  be- 
coming perfectly  clear  above  the  solid  sodium  sul- 
phate. Decant  this  clear  solution  (if  necessary 
through  a  dry  filter  paper)  into  a  dry  100-c.c. 
Erlenmeyer  flask.  Pass  a  rapid  current  of  dry  air 
(pass  through  CaCl2  tower)  into  the  mouth  of  the 
Erlenmeyer  flask  and  heat  to  a  temperature  below 
75°  C.  on  a  dry  hot  plate  until  the  ether  is  entirely 
driven  off. 

Note. — It  is  important  to  follow  all  of  the  details  since  ether  generally 
contains  alcohol  and  after  washing  with  water  always  contains  water.  It 
is  very  difficult  to  remove  water  and  alcohol  by  evaporation  from  fatty  acids, 
but  the  washing  of  the  ether  solution  and  subsequent  drying  with  anhydrous 
sodium  sulphate  removes  both  water  and  alcohol.  Ether,  in  the  absence  of 
water  and  alcohol,  is  easily  removed  from  fatty  acids  by  gentle  heat. 

The  fatty  acids  prepared  as  above  should  be  kept 
in  a  stoppered  flask  and  examined  at  once. 

(g)  Test  for  Mineral  Oil  and  Oilier  Unsaponifiable 

Matter 

Place  10  drops  of  the  fatty  acid  (/)  in  a  50-c.c. 
test  tube,  add  5  c.c.  of  alcoholic  soda  (see  re- 
agents), boil  vigorously  for  5  minutes,  add  40  c.c. 
of  water,  and  mix ;  a  clear  solution  indicates  that 
not  more  than  traces  of  unsaponifiable  matter  are 
present.  If  the  solution  is  not  clear,  the  oil  is  not 
pure  linseed  oil. 

(h)  Iodine  Number  of  Fatty  Acids 

Place  a  small  quantity  of  the  fatty  acids  (/)  in 
a  small  weighing  burette  or  beaker.  Weigh  accu- 


44         Chemical  Analysis  of  Lead  and  Its  Compounds 

rately.  Transfer  by  dropping  about  0.15  gram 
(0.10  to  0.20  gram)  to  a  500-c.c.  bottle  having  a 
well  ground  glass  stopper,  or  an  Erlenmeyer  flask 
having  a  specially  flanged  neck  for  the  iodine  test. 
Reweigh  the  burette  or  beaker  and  determine  the 
amount  of  sample  used.  Add  10  c.c.  of  chloroform. 
Whirl  the  bottle  to  dissolve  the  sample.  Add  10 
c.c.  of  chloroform  to  two  empty  bottles  like  that 
used  for  the  sample.  Add  to  each  bottle  25  c.c. 
of  the  Harius  solution  (see  reagents)  and  let  stand, 
with  occasional  shaking,  for  one-half  hour.  Add 
10  c.c.  of  the  15  per  cent  potassium  iodide  solution 
and  100  c.c.  of  water,  and  titrate  with  standard 
sodium  thiosulphate,  using  starch  as  indicator. 
The  titrations  on  the  two  blank  tests  should  agree 
within  0.1  c.c.  From  the  difference  between  the 
average  of  the  blank  titrations  and  the  titration 
on  the  sample  and  the  iodine  value  of  the  thiosul- 
phate solution,  calculate  the  iodine  number  of  the 
sample  tested.  (Iodine  number  is  centigrams  of 
iodine  to  1  gram  of  sample.)  If  the  iodine  number 
is  less  than  170,  the  oil  does  not  meet  the  specifi- 
cation. 


(i)  Coarse  Particles  and  "Skins" 

Weigh  an  amount  of  paste  containing  50  grams 
of  pigment  (see  2  (d)),  add  kerosene,  and  wash 
through  a  No.  200  screen  as  in  1  (c).  The  residue 
is  reported  as  "  Coarse  particles  and  skins, "  and 
should  weigh  less  than  0.25  gram. 


Zinc  Oxide  45 

Reagents 

(a)  Extraction  Mixture 

10  volumes  ether  (ethyl  ether). 
6  volumes  benzol. 
4  volumes  methyl  alcohol. 
1  volume  acetone. 

(b)  Aqueous  Sodium,  Hydroxide 

Dissolve  100  grams  sodium  hydroxide  in  dis- 
tilled water  and  dilute  to  300  c.c. 

(c)  Standard  Sodium  Thiosulphate  Solution 
Dissolve  pure  sodium  thiosulphate  in  distilled 

water  that  has  been  well  boiled  to  free  it  from  car- 
bon dioxide,  in  the  proportion  of  24.83  grams  crys- 
tallized sodium  thiosulphate  to  1000  c.c.  of  the 
solution.  It  is  best  to  let  this  solution  stand  for 
about  two  weeks  before  standardizing.  Standard 
ize  with  pure  resublimed  iodine.  (See  Analytical 
Chemistry,  Treadwell-Hall,  vol.  II,  3d  ed.,  p.  646.) 
This  solution  will  be  approximately  decinormal, 
and  it  is  best  to  leave  it  as  it  is  after  determining 
its  exact  iodine  value  rather  than  to  attempt  to 
adjust  it  to  exactly  decinormal.  Preserve  in  a 
stock  bottle  provided  with  a  guard  tube  filled  with 
soda  lime. 

(d)  Starch  Solution 

Stir  up  2  to  3  grams  of  potato  starch  or  5  grams 
soluble  starch  with  100  c.c.  of  1  per  cent  salicylic 
acid  solution,  add  300  to  400  c.c.  boiling  water,  and 
boil  the  mixture  until  the  starch  is  practically  dis- 
solved, then  dilute  to  1  liter. 


46        Chemical  Analysis  of  Lead  and  Its  Compounds 

(e)  Potassium  Iodide  Solution 

Dissolve  150  grams  of  potassium  iodide  free 
from  iodate  in  distilled  water  and  dilute  to 
1000  c.c. 

(f)  Hanus  Solution 

Dissolve  13.2  grams  of  iodine  in  1000  c.c.  of 
99.5  per  cent  glacial  acetic  acid  which  will  not 
reduce  chromic  acid.  Add  enough  bromine  to 
double  the  halogen  content,  determined  by  titra- 
tion  (3  c.c.  of  bromine  is  about  the  proper  amount). 
The  iodine  may  be  dissolved  by  the  aid  of  heat,  but 
the  solution  should  be  cold  when  the  bromine  is 
added. 

(g)  Alcoholic  Sodium  Hydroxide  Solution 

Dissolve  pure  sodium  hydroxide  in  95  per  cent 
ethyl  alcohol  in  the  proportion  of  about  22  grams 
per  1000  c.c.  Let  stand  in  a  stoppered  bottle.  De- 
cant the  clear  liquid  into  another  bottle  and  keep 
well  stoppered.  This  solution  should  be  colorless 
or  only  slightly  yellow  when  used,  and  it  will  keep 
colorless  longer  if  the  alcohol  is  previously  treated 
with  sodium  hydroxide  (about  80  grams  to  1000 
c.c.),  kept  at  about  50°  C.  for  15  days'  and  then 
distilled. 

(k)  Uranyl  Indicator  for  Zinc  Titration 

A  5  per  cent  solution  of  uranyl  nitrate  in  water 
or  a  5  per  cent  solution  of  uranyl  acetate  in  water 
made  slightly  acid  with  acetic  acid. 


Zinc  Oxide  47 

(i)  Standard  Potassium  Ferrocyanide 

Dissolve  22  grams  of  the  pure  salt  in  water  and 
dilute  to  1000  c.c.  To  standardize,  transfer  about 
0.2  gram  (accurately  weighed)  of  pure  metallic 
zinc  or  freshly  ignited  pure  zinc  oxide  to  a  400-c.c. 
beaker.  Dissolve  in  10  c.c.  hydrochloric  acid  and 
20  c.c.  water.  Drop  in  a  small  piece  of  litmus 
paper,  add  ammonium  hydroxide  until  slightly 
alkaline,  then  add  hydrochloric  acid  until  just  acid, 
and  then  add  3  c.c.  strong  hydrochloric  acid.  Di- 
lute to  about  250  c.c.  with  hot  water  and  heat  nearly 
to  boiling.  Run  in  the  f errocyanide  solution  slowly 
from  a  burette  with  constant  stirring  until  a  drop 
tested  on  a  white  porcelain  plate  with  a  drop  of 
the  uranyl  indicator  shows  a  brown  tinge  after 
standing  one  minute.  A  blank  should  be  run  with 
the  same  amounts  of  reagents  and  water  as  in  the 
standardization.  The  amount  of  ferrocyanide 
solution  required  for  the  blank  should  be  sub- 
tracted from  the  amounts  used  in  standardization 
and  in  titration  of  the  sample.  The  standardiza- 
tion must  be  made  under  the  same  conditions  of 
temperature,  volume,  and  acidity  as  obtain  when 
the  sample  is  titrated. 

(j)  Barium  Chloride  Solution 

Dissolve  100  grams  of  pure  crystallized  barium 
chloride  in  water  and  dilute  to  1000  c.c. 


CHAPTER    VI 

LITHOPONE1 

This  pigment  is  a  chemically  precipitated  pig- 
ment containing  approximately  from  69  to  70  per 
cent  barium  sulphate,  the  remainder  consisting  of 
zinc  sulphide,  with  occasional  impurities  of  fcine 
oxide  and  carbonate. 

Analysis 
Moisture 
Heat  2  grams  for  two  hours  at  105°  C. 

Barium  Sulphate 

Treat  1  gram  with  10  c.c.  cone.  HC1  and  1  gram 
of  potassium  chlorate,  added  in  small  amounts. 
Evaporate  to  one-half  its  volume,  add  100  c.c.  hot 
water  and  a  few  c.c.  of  dilute  H,SO4.  Boil,  filter, 
wash  and  weigh  the  insoluble  residue,  which  should 
show  only  the  presence  of  barium  sulphate.  Exam- 
ine the  residue  for  silica  and  alumina. 

Total  Zinc 

Determine  the  total  zinc  in  the  filtrate  by  the 
volumetric  method  as  outlined  under  Sublimed 
White  Lead. 


iStandard  Methods  of  Chemical  Analysis,  Scott,  p.  630. 

48 


Lithopone  49 

Zinc  Sulphide 

Digest  1  gram  at  room  temperature  for  one-half 
hour  with  100  c.c.  of  1  per  cent  acetic  acid.  Filter 
and  determine  the  zinc  in  the  precipitate  by  solu- 
tion in  HC1  as  under  Sublimed  White  Lead. 

Zinc  soluble  in  acetic  acid  is  reported  as  zinc 
oxide,  zinc  insoluble  as  zinc  sulphide.  The  filtrate 
from  the  acetic  acid  treatment,  after  precipitating 
the  zinc  as  zinc  sulphide  and  subsequent  removal, 
should  be  examined  for  barium  which  might  be 
present  as  carbonate,  and  calcium,  present  as  either 
sulphate  or  carbonate. 

U.  S.  Interdepartmental  Committee's  Recom- 
mended Laboratory  Examination  for 
Flat  Interior  Lithopone  Paint, 
White  and  Light  Tints1 

1.  Laboratory  Examination 
(a)  Caking  in  Container 

When  an  original  package  is  received  in  the  lab- 
oratory it  shall  be  weighed,  opened,  and  stirred 
with  a  stiff  spatula  or  paddle.  The  paint  must  be 
no  more  difficult  to  mix  to  a  uniform  consistency 
than  a  good  grade  of  flat  paint.  The  paint  shall 
finally  be  thoroughly  mixed,  removed  from  the  con- 
tainer, and  the  container  wiped  clean  and  weighed. 
This  weight  subtracted  from  the  weight  of  the  orig- 

1Prepared  and  recommended  by  the  U.  S.  Interdepartmental  Committee  on 
Paint  Specification  Standardization,  January  21,  1921.  P.  H.  Walker, 
Bureau  of  Standards,  Chairman ;  J.  W.  Cinder,  Treasury  Department, 
Secretary.  Circular  of  the  Bureau  of  Standards.  No.  111. 


50        Chemical  Analysis  of  Lead  and  Its  Compounds 

inal  package  gives  the  net  weight  of  the  contents. 
A  portion  of  the  thoroughly  mixed  paint  shall  be 
placed  in  a  clean  container  and  portions  for  the 
remaining  tests  promptly  weighed  out. 

(b)  Color 

Place  some  of  the  paint  on  a  clean,  clear  glass 
plate.  Place  some  of  the  standard  agreed  upon 
beside  the  sample  on  the  plate,  turn  the  glass  over, 
and  compare  the  colors. 

(c)  Weight  Per  Gallon 

Weigh  a  clean,  dry  100-c.c.  graduated  flask.  Fill 
to  the  mark  with  the  thorougly  mixed  paint  and 
weigh  again.  The  increase  in  weight  expressed  in 
grams,  divided  by  100,  gives  the  specific  gravity, 
which  multiplied  by  8.33  gives  the  weight  in  pounds 
per  gallon. 

(d)  Brushing  Properties,  Time  of  Drying,  and  Re- 
sistance to  Washing 

Brush  the  well  mixed  paint  on  a  suitable  panel 
which  may  be  ground  glass,  steel,  or  well  filled 
wood.  Note  whether  the  paint  works  satisfactorily 
under  the  brush.  Place  the  panel  in  a  vertical  posi- 
tion in  a  well-ventilated  room  and  let  it  stand  for 
18  hours.  The  paint  should  be  dry  and  free  from 
streaks.  Let  the  panel  stand  for  five  days,  then 
make  marks  on  it  with  a  soft  lead  pencil  (No.  2, 
Mogul)  and  wash  these  marks  off  with  warm  (75° 
C.)  distilled  water  and  white  floating  soap,  using 
a  sponge  or  soft  rag.  The  marks  must  be  removed 
by  this  treatment  without  appreciably  marring  the 
paint  film. 


Lithopone  51 

(e)  Fastness  to  Light 

Apply  a  sufficient  number  of  coats  of  the  paint 
to  a  ground  glass  plate  to  completely  hide  the  sur- 
face, cover  half  of  this  painted  surface  with  opaque 
black  paper,  and  expose  indoors  in  a  well  lighted 
room  for  five  days.  Remove  the  black  paper  and 
examine  the  surface.  The  exposed  portion  should 
be  no  darker  than  the  portion  protected  by  the 
black  paper. 

(f)  Water 

Mix  100  grams  of  the  paint  in  a  300-c.c.  flask 
with  75  c.c.  of  toluol.  Connect  with  a  condenser 
and  distill  until  about  50  c.c.  of  distillate  has  been 
collected  in  a  graduate.  The  temperature  in  the 
flask  should  be  then  about  105  to  110°  C.  The  num- 
ber of  cubic  centimeters  of  water  collecting  under 
the  toluol  in  the  receiver  is  the  percentage  of  water 
in  the  paint.  Material  complying  with  the  speci- 
fication should  yield  less  than  1.0  c.c. 

(g)  Volatile  Thinner 

Weigh  accurately  from  3  to  5  grams  of  the  paint 
into  a  tared  flat  bottomed  dish  about  5  cm.  in  diam- 
eter, spreading  the  paint  over  the  bottom.  Heat  at 
105  to  1.10°  C.  for  one  hour,  cool,  and  weigh.  Cal- 
culate the  loss  in  weight  as  percentage  of  water  and 
volatile  thinner,  subtract  from  this  the  percentage 
of  water  (1  (/) ),  and  report  the  remainder  as  vola- 
tile thinner. 
(h)  Percentage  of  Pigment 

Weigh  accurately  about  15  grams  of  the  paint 
into  a  weighed  centrifuge  tube.  Add  20  to  30  c.c. 


52         Chemical  Analysis  of  Lead  and  Its  Compounds 

of  "extraction  mixture "  (see  reagents),  mix  thor- 
oughly with  a  glass  rod,  wash  the  rod  with  more 
of  the  extraction  mixture,  and  add  sufficient  of  the 
reagent  to  make  a  total  of  50  c.c.  in  the  tube.  Place 
the  tube  in  the  container  of  a  centrifuge,  surround 
with  water,  and  counterbalance  the  container  of 
the  opposite  arm  with  a  similar  tube  or  a  tube  with 
water.  Whirl  at  a  moderate  speed  until  well  set- 
tled. Decant  the  clear  supernatant  liquid.  Repeat 
the  extraction  twice  with  40  c.c.  of  extraction  mix- 
ture and  once  with  40  c.c.  of  ether.  After  drawing 
off  the  ether,  set  the  tube  in  a  beaker  of  water  at 
about  80°  C.  or  on  top  of  a  warm  oven  for  10  min- 
utes, then  in  an  oven  at  110  to  115°  C.  for  two 
hours.  Cool,  weigh,  and  calculate  the  percentage 
of  pigment.  Grind  the  pigment  to  a  fine  powder, 
pass  through  a  No.  80  sieve  to  remove  any  skins, 
and  preserve  in  a  stoppered  bottle.  Preserve  the 
extracted  vehicle  for  1  (t). 

(i)  Percentage  of  Non-Volatile  Vehicle 

Add  together  the  percentages  of  water  (1  (/)), 
of  volatile  thinner  (1  (#)),  and  of  pigment  (1  (h)), 
and  subtract  the  sum  from  100.  The  remainder  is 
the  percentage  of  non-volatile  vehicle,  which 
should  be  not  less  than  one-third  as  large  as  the 
percentage  of  volatile  thinner. 

(j)  Nature  of  Non-Volatile  Vehicle 

Evaporate  the  extracted  vehicle  and  extraction 
mixture  from  1  (h)  to  about  5  c.c.  Thoroughly 
clean  with  benzol  a  piece  of  bright  sheet  iron,  tin 
plate,  or  terneplate.  Spread  a  portion  of  the  con- 


Lithopone  53 

centrated  extracted  vehicle  on  the  sheet  of  metal, 
allow  to  dry  for  30  minutes  at  room  temperature 
in  a  vertical  position,  bake  for  three  hours  at  100 
to  110°  C.  (212  to  221°  F.),  remove  from  the  oven, 
and  keep  at  room  temperature  for  three  days.  Test 
the  film  with  a  knife  blade  at  a  place  not  less  than 
2.5  cm.  (1  inch)  from  the  edge.  The  film  should 
be  tough  and  elastic ;  if  it  powders  or  if  particles 
fly  under  the  test,  it  will  be  considered  brittle, 
which  will  be  cause  for  rejection.  The  film  must 
also  stand  light,  vigorous  rubbing  with  the  finger 
without  powdering  or  disintegrating. 

(k)  Coarse  Particles  and  "Skins" 

Dry  in  an  oven  at  105  to  110°  0.  a  No.  200  sieve, 
cool,  and  weigh  accurately.  Weigh  an  amount  of 
paint  containing  30  grams  of  pigment  (see  1  (/&)), 
add  50  c.c.  of  kerosene,  mix  thoroughly,  and  wash 
with  kerosene  through  the  sieve,  breaking  up  all 
lumps,  but  not  grinding.  After  washing  with  kero- 
sene until  all  but  the  particles  too  coarse  to  pass 
the  sieve  have  been  washed  through,  wash  all  kero- 
sene from  the  sieve  with  ether  or  petroleum  ether, 
heat  the  sieve  for  one  hour  at  105  to  110°  C.,  cool, 
and  weigh.  The  total  residue  left  on  the  sieve 
should  be  not  more  than  0.15  gram. 

2.  Analysis  of  Pigment 
Use  the  pigment  extracted  in  1  (h). 

(a)  Qualitative  Analysis 

Make  qualitative  analysis  following  ordinary 
methods. 


54         Chemical  Analysts  of  Lead  and  Its  Compounds 

(b)  Matter  Soluble  in  Water 

Transfer  2.5  grams  of  the  pigment  to  a  grad- 
uated 250-c.c.  flask,  add  100  c.c.  of  water,  boil  for 
five  minutes,  cool,  fill  to  mark  with  water,  mix,  and 
allow  to  settle.  Pour  the  supernatant  liquid 
through  a  dry  filter  paper  and  discard  the  first 
20  c.c.  Then  evaporate  100  c.c.  of  the  clear  filtrate 
to  dryness  in  a  weighed  dish,  heat  for  one  hour  at 
105  to  110°  C.,  cool,  and  weigh.  The  residue  should 
not  exceed  0.008  gram. 

(c)  Barium  Sulphate  and  Siliceous  Material 

Transfer  1  gram  of  pigment  to  a  porcelain  cas- 
serole or  dish,  moisten  with  a  few  drops  of  alcohol, 
add  40  c.c.  of  hydrochloric  acid  (1.1,  specific  grav- 
ity), cover,  and  boil  to  expel  hydrogen  sulphide; 
remove  the  cover  and  evaporate  to  dryness  on  the 
steam  bath,  moisten  with  hydrochloric  acid,  dilute 
with  water,  filter  through  paper,  and  wash  with 
dilute  hydrochloric  acid  and  then  with  hot  water 
until  the  washings  are  free  from  zinc  and  chlorine. 
Ignite  and  weigh  the  residue,  which  will  be  barium 
sulphate  and  siliceous  material. 

Mix  the  ignited  residue  with  about  10  times  its 
weight  of  anhydrous  sodium  carbonate  (grind  the 
mixture  in  an  agate  mortar  if  necessary),  fuse  the 
mixture  in  a  covered  platinum  crucible,  heating 
about  one  hour.  Let  cool,  place  the  crucible  and 
cover  in  a  250-c.c.  beaker,  add  about  100  c.c.  of 
water,  and  heat  until  the  melt  is  disintegrated. 
Filter  on  paper  (leaving  the  crucible  and  cover 
in  the  beaker)  and  wash  the  beaker  and  filter  thor- 


Lithopone  55 

oughly  with  hot  water  to  remove  soluble  sulphates. 
Place  the  beaker  containing  the  crucible  and  cover 
under  the  funnel,  pierce  the  filter  with  a  glass  rod, 
and  wash  the  carbonate  residue  into  the  beaker 
by  means  of  a  jet  of  hot  water.  Wash  the  paper 
with  hot  dilute  hydrochloric  acid  (1:1),  and  then 
with  hot  water.  If  the  carbonate  residue  is  not 
completely  dissolved,  add  sufficient  dilute  hydro- 
chloric acid  to  effect  solution,  and  remove  the  cru- 
cible and  cover,  washing  them  with  a  jet  of  water. 
Heat  the  solution  to  boiling  and  add  10  to  15  c.c. 
of  dilute  sulphuric  acid,  and  continue  the  boiling 
for  10  or  15  minutes  longer.  Let  the  precipitate 
settle,  filter  on  a  weighed  Gooch  crucible,  wash 
with  hot  water,  ignite,  cool,  and  weigh  as  BaS04. 
Subtract  from  the  result  of  the  previous  deter- 
mination to  obtain  the  siliceous  material. 

(d)  Total  Zinc  Calculated  as  Zinc  Oxide 

With  material  containing  no  interfering  ele- 
ments (iron,  for  example),  weigh  accurately  about 
1  gram  of  pigment,  transfer  to  a  400-c.c.  beaker, 
moisten  with  alcohol,  add  30  c.c.  of  hydrochloric 
acid  (1:2),  boil  for  two  to  three  minutes,  add  200 
c.c.  of  water  and  a  small  piece  of  litmus  paper ;  add 
strong  ammonia  until  slightly  alkaline,  render  just 
acid  with  hydrochloric  acid,  then  add  3  c.c.  of 
strong  hydrochloric  acid,  heat  nearly  to  boiling, 
and  titrate  with  standard  ferrocyanide  as  in  stand- 
ardizing that  solution  (see  reagents).  Calculate 
total  zinc  as  zinc  oxide. 


56         Chemical  Analysis  of  Lead  and  Its  Compounds 

When  iron  or  other  interfering  elements  are 
present  (see  2  (a)),  take  the  filtrate  containing 
the  zinc  from  2  (c),  add  a  slight  excess  of  bromine 
water  and  2  grams  ammonium  chloride,  heat  to 
nearly  boiling,  add  an  excess  of  ammonia,  heat  for 
about  two  minutes,  filter,  dissolve  the  precipitate 
in  hydrochloric  acid,  add  2  grams  of  ammonium 
chloride,  and  reprecipitate  with  ammonia  as  above. 
Filter,  wash  the  precipitate  with  hot  2  per  cent 
ammonium  chloride  solution,  unite  the  two  fil- 
trates, and  determine  zinc  as  above. 

(e)  Zinc  Oxide 

Weigh  accurately  2.5  grams  of  pigment,  trans- 
fer to  a  250-c.c.  graduated  flask,  moisten  with  a  few 
drops  of  alcohol,  add  about  200  c.c.  of  1  to  3  per 
cent  acetic  acid,  shake  vigorously  and  let  stand  for 
30  minutes,  shaking  once  every  five  minutes.  Fill 
to  the  mark  with  1  to  3  per  cent  acetic  acid,  mix, 
filter  through  a  dry  paper,  discard  the  first  25  c.c., 
and  determine  zinc  in  100  c.c.  of  the  filtrate  (cor- 
responding to  1  gram)  as  in  2  (d).  Calculate  the 
percentage  of  zinc  oxide. 

(f)  Calculations 

Subtract  the  percentage  of  zinc  oxide  (2  (e)) 
from  the  percentage  of  total  zinc  as  zinc  oxide  (2 
(d))  and  multiply  the  remainder  by  1.2  to  convert 
to  percentage  of  zinc  sulphide.  In  case  the  percent- 
age of  barium  sulphate  (2  (c))  is  not  more  than 
2.86  times  as  great  as  the  percentage  of  zinc  sul- 
phide, add  the  two  together  and  call  the  sum  the 


Lithopone  57 

percentage  of  lithopone.  If  the  percentage  of  ba- 
rium sulphate  is  greater  than  this  amount  take 
2.86  times  the  percentage  of  zinc  sulphide  as  the 
percentage  of  barium  sulphate  to  be  included  in  the 
percentage  of  lithopone  and  include  the  remainder 
in  the  percentage  of  tinting  and  extending  pig- 
ments. Subtract  the  sum  of  the  percentages  of 
zinc  oxide  (2  (e)),  lithopone,  and  matter  soluble 
in  water  (2  (b))  from  100.  Call  the  remainder 
percentage  of  tinting  and  extending  pigments. 

3.  Reagents 

(a)  Extraction  Mixture 

10  volumes  ether  (ethyl  ether). 
6  volumes  benzol. 
4  volumes  methyl  alcohol. 
1  volume  acetone. 

(b)  One  to  Three  Per  Cent  Acetic  Acid 

Dilute  20  c.c.  glacial  acetic  acid  to  1000  c.c.  with 
distilled  water. 

(c)  Uranyl  Indicator  for  Zinc  Titration 

A  5  per  cent  solution  of  uranyl  nitrate  in  water 
or  a  5  per  cent  solution  of  uranyl  acetate  in  water 
made  slightly  acid  with  acetic  acid. 

(d)  Standard  Potassium  Ferrocyanide 
Dissolve  22  grams  of  the  pure  salt  in  water  and 

dilute  to  1000  c.c.  To  standardize,  transfer  about 
0.2  gram  (accurately  weighed)  of  pure  metallic 
zinc  or  freshly  ignited  pure  zinc  oxide  to  a  400-c.c. 
beaker.  Dissolve  in  10  c.c.  of  hydrochloric  acid 


X 
58         Chemical  Analysis  of  Lead  and  Its  Compounds 

and  20  c.c.  of  water.  Drop  in  a  small  piece  of  lit- 
mus paper,  add  ammonium  hydroxide  until  slightly 
alkaline,  then  add  hydrochloric  acid  until  just  acid, 
and  then  3  c.c.  of  strong  hydrochloric  acid.  Dilute 
to  about  250  c.c.  with  hot  water  and  heat  nearly  to 
boiling.  Run  in  the  ferrocyanide  solution  slowly 
from  a  burette  with  constant  stirring  until  a  drop 
tested  on  a  white  porcelain  plate  with  a  drop  of  the 
uranyl  indicator  shows  a  brown  tinge  after  stand- 
ing one  minute.  A  blank  should  be  run  with  the 
same  amounts  of  reagents  and  water  as  in  the 
standardization.  The  amount  of  ferrocyanide 
solution  required  for  the  blank  should  be  sub- 
tracted from  the  amounts  used  in  standardization 
and  in  titration  of  the  sample.  The  standardiza- 
tion must  be  made  under  the  same  conditions  of 
temperature,  volume  and  acidity  as  obtain  when 
the  sample  is  titrated. 


CHAPTEK    VII 

A     COLORIMETRIC     METHOD     FOR     THE 

DETERMINATION  OF   COPPER  AND 

IRON  IN  PIG  LEAD,  LEAD  OXIDES, 

AND  LEAD  CARBONATE1 

Most  methods  in  use  for  the  determination  of  the 
small  percentage  of  copper  contained  in  pig  lead, 
lead  oxides  and  lead  carbonate  are  long  and  tedious. 
This  is  especially  true  in  those  instances  where 
refined  metal  serves  as  the  base  for  the  finished 
product  and  the  copper  content  being  extremely 
low,  many  difficulties  present  themselves;  these 
can  be  overcome  by  the  use  of  this  colo  rime  trie 
method. 

While  the  estimation  of  the  iron  content  in  these 
compounds  can  be  readily  carried  out  colorimet- 
rically  by  a  separate  analysis,2  it  has  been  found 
that  the  following  method,  which  combines  the 
determination  of  both  copper  and  iron  colorimet- 
rically  in  one  analysis,  adds  greatly  to  the  rapidity 
and  accuracy  in  finding  the  percentages  of  these 
impurities.  The  method  not  only  eliminates  the 
use  of  hydrogen  sulphide,  but  it  shortens  the  time 
of  a  single  analysis  to  30  or  40  minutes,  while  the 
results  attain  the  same  degree  of  accuracy  as  those 

ij.  Ind.  Eng.  Chem.,  1,  1035  (1915). 
2J.  Ind.  Eng.  Chem.,  4,  659  (1912). 

59 


60         Chemical  Analysis  of  Lead  and  Its  Compounds 

established  by  the  longer  and  more  complicated 
methods. 

The  method  of  procedure  varies  somewhat  with 
the  nature  of  the  sample  to  be  examined:  hence, 
it  will  be  necessary  to  make  especial  mention  of 
red  lead. 


Analysis  of  Pig  Lead,  Litharge  and 
Lead  Carbonate  for  Copper 

Weight  of  Sample 

In  analyzing  refined  pig  lead,  or  lead  compounds 
made  from  refined  metals,  it  is  necesary,  owing  to 
the  small  percentages  of  copper  and  iron  usually 
present,  to  use  large  samples.  It  has  been  found, 
by  the  use  of  this  method,  that  smaller  samples 
may  be  used  with  equally  accurate  results,  thereby 
reducing  the  bulk  to  be  handled  and  eliminating 
any  errors  which  frequently  result  from  the  use 
of  large  volumes.  A  sample  weighing  30  grams 
has  been  found  sufficiently  large  for  refined  prod- 
ucts, and  not  over  10  grams  need  be  used  for  the 
crude  or  unrefined  material. 

Method  of  Procedure 

Weigh  the  finely  divided  sample  into  a  400-c.c. 
beaker,  and  add  small  portions  of  hot  (1:1)  nitric 
acid  until  solution  is  effected.  If  any  basic  lead 
nitrate  has  been  formed,  dilute  slightly  with 
warm  water  and  boil.  Add  32  c.c.  (1:1)  sul- 
phuric acid,  stirring  constantly  while  adding.  Let 


Colorimetric  Method  for  Copper  and  Iron  61 

the  precipitate  settle,  and  decant  filtrate  through 
a  coarse  filter  paper.  Wash  four  times  by  de- 
cantation,  using  small  portions  of  warm,  dis- 
tilled water.  Transfer  the  precipitate  to  the 
paper,  wash  again  and  allow  to  drain.  Make  the 
filtrate  neutral  with  ammonium  hydroxide  and  add 
4  c.c.  excess.  Boil  for  a  short  time  and  filter.  Wash 
the  precipitate  well  with  warm  water,  and  reserve 
for  the  determination  of  the  iron.  Render  the  fil- 
trate acid  with  special  c.  p.  hydrochloric  acid,  add- 
ing not  more  than  two  drops  excess.  Add  six  drops 
of  (1:10)  potassium  ferrocyanide  solution,  filter 
through  close  filter  papers  using  two  to  each  funnel. 
Catch  the  filtrate  and  inspect  for  copper  ferrocy- 
anide. Let  the  precipitate  drain  well  without  wash- 
ing. Dissolve  the  copper  ferrocyanide  off  of  the 
paper  with  alternate  washings  of  small  portions  of 
ammonium  hydroxide  and  hot  water.  Wash  well 
and  keep  the  bulk  to  30  or  40  c.c.  Render  slightly 
acid  with  hydrochloric  acid,  adding  not  over  two 
drops  excess.  Transfer  to  a  100-c.c.  Nessler  tube, 
and  dilute  to  mark  with  distilled  water.  The  copper 
is  then  determined  colorimetrically  according  to  a 
modification  of  the  method  of  Carnelly.1 

In  another  Nessler  tube,  place  10  c.c.  of  5  per  cent 
ammonium  nitrate  solution,  two  drops  concen- 
trated nitric  acid  and  90  c.c.  distilled  water,  add 
from  a  burette  graduated  to  tenths  of  1  c.c.,  stand- 
ard copper  sulphate  solution  until  the  color 
matches  the  sample  under  examination. 


iSutton's  Volumetric  Analysis,  p.  204. 


62        Chemical  Analysis  of  Lead  and  Its  Compounds 
Standard  Copper  Sulphate  Solution1 

"Dissolve  0.393  gram  of  pure  CuS04.5ILO,  in 
one  liter  of  distilled  water.  1  c.c.  ==  0.0001  gram 
of  copper, "  or  0.00033  per  cent  when  using  a  30 
gram  sample. 

Analysis  of  Red  Lead  for  Copper 

Treat  30  grams  of  the  sample  with  40  c.c.  (1:1) 
nitric  acid,  using  great  care  that  the  violence  of 
the  reaction  does  not  cause  the  sample  to  froth 
over  the  beaker.  Slowly  add  30  to  40  c.c.  of  3  per 
cent  hydrogen  peroxide,  stirring  constantly.  Boil 
until  solution  is  effected,  and  proceed  as  directed 
under  the  "Analysis  of  Pig  Lead,"  on  page  60. 

Sodium  sulphite  c.  p.  may  be  used  in  place  of  the 
hydrogen  peroxide  for  effecting  the  solution  of  lead 
peroxide,  adding  it  dry  in  small  portions  and  boil- 
ing until  no  brown  lead  peroxide  is  present. 

Determination  of  Iron  in  the  Above 
Compounds 

For  the  iron  determination,  use  the  precipitate 
of  iron  hydroxide  removed  from  the  copper  solu- 
tion, proceeding  as  follows :  Dissolve  the  precipi- 
tate contained  on  the  paper  with  (1 :1)  hydrochloric 
acid,  collecting  the  filtrate  in  a  300-c.c.  volumetric 
flask.  Wash  the  paper  free  from  acid  with  hot, 
x  distilled  water,  dilute  to  mark,  and  mix  thoroughly. 

iSutton's  Volumetric  Analysis,  p.  205. 


Colorimetric  Method  for  Copper  and  Iron  63 

Place  10  c.c.  in  a  100-c.c.  Nessler  tube,  add  three 
drops  nitric  acid,  10  c.c.  (1:15)  ammonium  sul- 
phocyanide  solution,  dilute  to  mark  and  compare 
with  a  standard  iron  solution  according  to  the 
method  outlined  by  Schaeffer  i1 

"The  color  is  compared  with  a  blank  made  in 
the  following  manner:  A  solution  of  ferric  am- 
monium sulphate  of  known  strength  is  required. 
This  is  made  by  dissolving  0.7022  gram  of  ferrous 
ammonium  sulphate  in  water.  Acidify  with  sul- 
phuric acid,  heat  to  boiling  and  add  a  solution  of 
potassium  permanganate  until  all  the  iron  is  con- 
verted to  the  ferric  condition.  Only  the  very  slight- 
est pink  tinge  may  be  present  after  the  addition  of 
the  potassium  permanganate,  as  this  tinge  will 
fade  away,  while  the  presence  of  a  pink  color  tends 
to  vitiate  the  results.  Allow  the  solution  to  cool 
and  dilute  to  one  liter.  One  c.c.  of  this  solution 
equals  0.0001  gram  of  iron. 

Prepare  the  blank  by  pouring  into  a  100-c.c. 
Nessler  cylinder,  10  c.c.  ammonium  sulphocyanide 
solution,  and  three  drops  of  concentrated  nitric 
acid.  Dilute  to  100  c.c.  and  titrate  to  the  exact 
color  developed  in  the  sample  under  examination, 
by  the  addition  of  the  standard  ferric  ammonium 
sulphate  solution.  One  c.c.  of  this  solution  equals 
0.01  per  cent  iron  as  the  10  c.c.  removed  from  the 
flask  contained  1  gram  sample.  It  will  be  found 
that  the  color  can  be  accurately  compared  to  with- 
in 0.001  per  cent  of  iron  content. ' ' 

ij.  Ind.  &  Eng.  Chem.,  4  (1912),  650. 


LITHARGE  AND 

CiSO4  SOLUTION 

RED  LEAD 

%  Cu 

Fres. 

Color. 

Fres. 

Color. 

present 

0.002 

0.002 

0.002 

0.002 

0.002 

0.0008 

0.0008 

0.0008 

0.0008 

0.0008 

0.0009 

0.00088 

0.00066 

0.00066 

0.0007 

0.0007 

0.0007 

0.001 

0.001 

0.001 

0.0015 

0.0015 

0.00066 

0.00066 

0.00066 

0.0038 

0.0038 

0.0015 

0.0015 

0.0015 

0.00088 

0.00088 

0.00088 

0.00088 

0.00088 

0.00088 

0.0009 

0.0009 

0.00088 

0.0009 

0.0013 

0.0013 

0.0015 

0.0015 

0.0015 

0.00066 

0.00066 

0.0007 

0.00066 

0.0007 

64         Chemical  Analysis  of  Lead  and  Its  Compounds 
Comparison  of  Results  on  Copper 

Table  I  shows  the  results  obtained  by  the  above 
method,  as  compared  with  the  method  set  forth  by 
Fresenius,1  on  two  sets  of  samples  and  a  copper 
sulphate  solution  of  known  strength. 

TABLE  I— COMPARATIVE   RESULTS  (PERCENTAGES  Cu)  BY   METHOD  OK 
FRESENIUS  AND  OF  AUTHOR. 

PIG  LEAD 

No.  Fres.  Color. 

1 0.0009  0.00088 

2 0.0013  0.0013 

3 0.0009  0.00088 

4 0.002  0.002 

5 0.001  0.001 

6 0.0015  0.0015 

7 0.0012  0.0012 

8 0.0079  0.0079 

9 0.0013  0.0013 

10 0.0004  0.0004 

Precautions  and  Interfering  Elements 

If  the  sample  contains  much  zinc,  the  following 
method  may  be  used  for  removing  it :  The  filtrate 
from  the  iron  precipitation,  before  precipitating 
the  copper  ferrocyanide,  is  rendered  slightly  acid 
with  acetic  acid,  and  5  c.c.  of  an  8  per  cent  sodium 
ammonium  phosphate  solution  are  added;  boil, 
cool,  filter  and  treat  the  filtrate  as  before  outlined. 

Lead,  when  present  in  not  too  large  quantity,  has 
little  or  no  effect  on  the  accuracy  of  the  colorimetrie 
comparison  of  copper.  If  a  faint  white  cloud  of 
lead  ferrocyanide  should  develop  in  the  sample 
under  examination,  the  addition  of  a  small  amount 
cf  very  dilute  lead  nitrate  solution  to  the  standard 
will  overcome  this  difficulty. 


iFresenius'  Quantitative  Chemical  Analysis,  Vol.  II,  p.  584. 


Colorimetric  Method  for  Copper  and  Iron  65 

Reagents  and  Indicators 

This  method  presupposes  the  use  of  absolutely 
pure  reagents,  especially  free  from  iron  and  cop- 
per .  Use  litmus  paper  as  an  indicator,  as  all  other 
indicators,  once  introduced,  will  affect  the  final 
color. 


CHAPTER    VIII 

RED  LEAD  AND  ORANGE  MINERAL 

These  two  compounds  are  oxides  of  lead,  of  an 
approximate  formula,  Pb.,O4,  being  probably  a 
combination  of  lead  dioxide  and  lead  monoxide. 
They  are  found  on  the  market  as  milled  oxides 
and  flake  oxides.  In  some  instances  oxides  are 
found  which  are  artificially  colored  with  organic 
dyes. 

Analysis 

The  analysis  of  red  lead  and  orange  mineral 
consists  in  the  determination  of  the  red  lead  con- 
tent or  the  lead  dioxide  content,  moisture,  iron, 
silica,  copper  and  metallic  lead.  It  is  also  neces- 
sary to  determine  from  a  physical  standpoint  the 
apparent  gravity  or  density,  which  may  be  done 
by  determining  the  weight  of  a  cubic  inch  of  the 
material,  as  outlined  on  page  148. 

Moisture 

Dry  2  grams  of  the  sample  for  2  hours  at  105°  C. 
The  loss  will  be  moisture. 

Red  Lead,  or  Lead  Dioxide1 

Treat  1  gram  of  the  sample  in  a  beaker  with  15 
c.c.  of  nitric  acid,  specific  gravity  1.2  (110  c.c.  nitric 
acid,  specific  gravity  1.42,  to  100  c.c.  of  water.  This 
solution  should  be  aerated  to  free  it  from  all 
nitrous  fumes). 

ij.  Ind.  Eng.  Chem.,  8,  237  (1916). 


Red  Lead  and  Orange  Mineral  67 

Stir  the  sample  until  all  trace  of  red  color  has 
disappeared.  Add  from  a  calibrated  pipette  or 
burette  exactly  10  c.c.  of  dilute  hydrogen  perox- 
ide (1  part  of  3  per  cent  hydrogen  peroxide  to 
3.5  parts  of  water).  Add  about  50  c.c.  of  hot 
water  and  stir  until  all  the  lead  dioxide  has 
passed  into  solution.  In  the  case  of  some  coarsely 
ground  oxides  the  contents  of  the  beaker  may  have 
to  be  gently  heated  to  effect  complete  solution. 
After  the  oxide  has  completely  passed  into  solu- 
tion, dilute  with  hot  water  to  about  250  c.c.  volume 
and  titrate  directly  with  a  standard  potassium 
permanganate  solution,  having  an  iron  value  of 
0.005.  Titrate  to  the  faint  pink  permanganate 
color.  A  blank  titration  on  the  hydrogen  peroxide 
solution  must  now  be  made. 

Titration  of  Hydrogen  Peroxide,  and  Calculation 
of  Results 

Into  a  beaker  pour  15  c.c.  of  nitric  acid  having 
the  strength  as  above  given  and  add  exactly  the 
same  amount  of  hydrogen  peroxide  (10  c.c.). 
Dilute  to  250  c.c.  with  hot  water  and  titrate  with 
standard  potassium  permanganate  to  a  faint  pink 
color. 

The  difference  between  the  number  of  cubic  cen- 
timeters of  potassium  permanganate  required  for 
the  blank  titration  and  the  number  required  for  the 
red  lead  titration  is  the  amount  of  potassium  per- 
manganate required  for  the  hydrogen  peroxide 
which  was  reacted  on  by  the  lead  dioxide.  The  dif- 
ference between  the  two  amounts  of  potassium 


68        Chemical  Analysis  of  Lead  and  Its  Compounds 

permanganate  required  multiplied  by  3.058  gives 
the  percentage  of  red  lead  present  according  to  the 
following  proportion: 

Let  X  ==  %  Pb;{04  per  c.c.  difference 
2Fe:Pb304::0.005:X 
112 :  685 : :  0.005 :  X 
X  equals  3.058 

To  determine  the  lead  dioxide  present  multiply 
this  difference  by  1.067  according  to  the  following 
proportion : 

Let  Y  ==  %  PbO,  per  c.c.  difference 
2Fe:PbOL,::0.005:Y 
112 :  239 : :  0.005 :  Y 
Y  equals  1.067 

These  calculations  have  been  arranged  in  a  series 
so  devised  as  to  permit  the  direct  reading  of  the 
red  lead  percentage.  The  basis  of  the  calculations 
depends  on  the  fact  that  each  c.c.  of  potassium 
permanganate  solution  (iron  value,  0.005)  is 
equivalent  to  3.058  per  cent  of  true  red  lead ;  or, 
each  0.1  c.c.  is  equivalent  to  0.3058  per  cent  true 
red  lead  on  a  one  gram  sample. 

A  red  lead  or  orange  mineral  having  100  per  cent 
true  red  lead  content  requires  32.7  c.c.  potassium 
permanganate  solution  of  the  above  strength. 

The  calculation,  therefore,  arranges  itself  as  fol- 
lows :  Each  0.1  c.c.  on  the  selected  burette  repre- 
sents 0.3058  per  cent  true  red  lead.  The  number 
32.7  being  equivalent  to  100  per  cent  occupies  an 
analogous  position  on  the  chart.  A  representative 


34.1 
33.9 
33.7 
33.5 
33.3 
33.1 
32.9 

32.7 
99.69 

99.07 
98.46 
97.85 
97.24 
96.63 
96.01 
95.40 
94.79 
94.18 
93.57 
92.96 
92.35 
91.74 


34.2 

34.0 


32.8 


99.38 
98.77 
98.16 
97.55 
96.94 
96.32 
95.71 
95.10 
94.49 
93.88 
93.26 
^92.66 
92.04 
91.43 


FIG.  1 


70        Chemical  Analysis  of  Lead  and  Its  Compounds 

portion  of  the  series  is  shown  alongside  of  figure 
one.  The  series  continues  upward  in  steps  of  0.1 
and  downward  in  steps  of  0.30  and  0.31  to  such 
points  as  are  required  for  the  red  lead  usually  ex- 
amined. 

Fig.  1  is  an  illustration  of  the  apparatus  in  use ; 
calculations  should  be  continued  upward  to  40.0  or 
to  that  point  where  the  hydrogen  peroxide  solution 
used  is  of  such  strength  that  10  c.c.  of  the  hydro- 
gen peroxide  solution  require  40  c.c.  of  the  potas- 
sium permanganate  solution.  Calculations  should 
be  continued  downward  to  9.48  per  cent  true  red 
lead  content. 

In  using  the  series  the  chart  is  attached  to  the 
burette  by  a  screw  clamp.  The  blank  determination 
is  first  made  on  the  hydrogen  peroxide  solution  and 
the  value  found  is  placed  opposite  zero  on  the 
burette.  In  the  analysis  of  the  red  lead  the  value 
is  then  read  off  directly.  As  a  hypothetical  case  we 
will  use  a  hydrogen  peroxide  solution  with  a  blank 
titration  of  34.1  c.c.  In  the  analysis  of  a  red  lead 
or  orange  mineral  4.2  c.c.  of  the  potassium  per- 
manganate solution  is  required  for  a  final  titration 
value.  The  calculation  shows  the  difference  be- 
tween the  two  readings  to  be  29.9  c.c.  or  multiplied 
by  3.058  equals  a  true  red  lead  percentage  of  91.43 
per  cent.  Comparing  this  with  the  series  of  calcu- 
lations we  find  4.2  c.c.  from  the  34.1  to  be  91.43  per 
cent. 

Should  it  be  preferred  to  determine  the  lead 
peroxide  content,  the  calculation  will  be  based  on 


Red  Lead  and  Orange  Mineral  71 

the  value  0.1067  for  each  0.1  c.c.  of  the  potassium 
permanganate  solution.  It  is  understood  that  the 
division  must  be  made  to  correspond  to  the  0.1  c.c. 
divisions  on  the  burette. 

It  is  always  advisable  to  make  several  blank  de- 
terminations each  day  where  this  analysis  is  con- 
stantly made  and  when  only  occasionally  used  a 
blank  titration  should  be  made  before  each  analysis. 

The  strength  of  the  hydrogen  peroxide  solution 
will  vary  but  the  permanance  of  the  permanganate 
solution  renders  the  method  accurate  over  a  long 
period  of  time. 

Standard  Potassium  Permanganate 
It  is  necessary  to  always  have  a  potassium 
permanganate  solution  with  an  iron  value  of  ex- 
actly 0.005  if  the  method  described  for  red  lead  is 
used.  Dissolve  5.75  grains  c.  p.  salt  in  two  liters 
distilled  water  and  store  in  a  brown  bottle  in  a  dark 
place  for  a  week  or  more.  By  this  time  all  organic 
matter  will  have  been  oxidized  and  after  filtering 
the  solution  through  an  asbestos  filter  the  solution 
is  ready  for  standardization.  As  small  amounts  of 
Mn02  destroy  the  permanence  of  this  solution,  it  is 
necessary  that  it  be  removed  by  filtering.  The 
method  described  in  Bureau  of  Standards  Circular 
No.  40  should  be  used.  This  method  is  as  follows : 
In  a  400-c.c.  beaker,  0.25  gram  of  sodium  oxalate 
is  dissolved  in  200  to  225  c.c.  of  hot  water  (80-90° 
C.)  and  10  c.c.  of  (1:1)  sulphuric  acid  added.  The 
solution  is  at  once  titrated  with  the  solution  of  per- 
manganate, the  solution  being  stirred  continuously 


72         Chemical  Analysis  of  Lead  and  Its  Compounds 

and  vigorously.  The  permanganate  must  be  added 
at  the  rate  of  10  to  15  c.c.  per  minute  and  the  last 
0.5  to  1  c.c.  must  be  added  drop  by  drop,  each  drop 
being  allowed  to  decolorize  fully  before  the  next 
is  added.  The  solution  should  not  be  below  60°  C. 
by  the  time  the  titration  is  completed.  With  a  per- 
manganate solution  having  an  iron  value  of  0.01)5 
per  c.c.,  41.66  c.c.  of  the  permanganate  are  required 
to  react  with  0.25  gram  sodium  oxalate. 

If  the  first  titration  shows  that  the  solution  is 
too  strong  a  small  amount  of  distilled  water  should 
be  added.  To  calculate  exactly  how  much  water  to 
add  divide  41.66  by  the  number  c.c.  required  in  the 
titration  and  multiply  by  the  number  of  c.c.  re- 
maining in  the  bottle.  The  difference  between  this 
product  and  the  number  of  c.c.  in  the  bottle  will 
be  the  volume  of  water  to  add. 

If  the  solution  is  too  weak  this  difference  multi- 
plied by  0.00283  will  be  the  grains  of  potassium 
permanganate  salt  to  add.  After  the  addition  of 
water  or  salt  the  solution  should  again  be  titrated 
and  if  a  titer  of  41.66  is  not  obtained  water  or  salt 
added  until  this  titer  is  obtained.  A  solution  care- 
fully prepared  in  this  manner  should  keep  for 
months. 

Flake  Red  Lead 

In  certain  instances  it  is  found  that  flake  red 
lead  is  soluble  only  with  the  greatest  difficulty  by 
the  above  procedure.  In  cases  where  this  difficulty 
is  encountered  the  following  method  will  be  found 
to  give  excellent  results : 


Red  Lead  and  Orange  Mineral  73 

Digest  1  gram  of  the  sample  in  a  beaker  with  15 
c.c.  of  nitric  acid  made  up  of  a  strength  as  given 
in  the  previous  method.  Boil  the  solution  for  a 
short  time,  add  10  c.c  of  a  standard  oxalic  acid 
solution,  the  strength  of  which  has  been  previously 
determined.  Add  2  c.c.  of  sulphuric  acid  (1:1). 
Boil  the  solution  and  titrate  with  a  standard  solu- 
tion of  potassium  permanganate  having  an  iron 
value  of  0.005.  A  blank  titration  on  the  same 
amount  of  oxalic  acid  must  be  made.  The  differ- 
ence between  the  amount  of  potassium  permanga- 
nate required  for  the  blank  titration  and  that  re- 
quired for  the  red  lead  titration  multiplied  by  the 
factor  3.058  or  1.067  will  give  the  content  of  red 
lead  or  lead  dioxide  according  to  the  proportions  in 
the  previous  analysis. 

Iron 

The  iron  should  be  determined  color imetrically 
as  described  on  page  62. 

Copper 

This  constituent  may  be  determined  gravimet- 
rically,  or  colorimetrically. 

By  the  gravimetric  method  twenty  grams  of  the 
sample  are  treated  in  a  large  beaker  with  50  c.c. 
of  nitric  acid,  25  c.c.  of  water  and  sufficient  hydro- 
gen peroxide  to  cause  complete  solution  of  the  lead 
dioxide. 

Determine  the  copper  as  outlined  under  the 
Analysis  of  Litharge. 

The  colorimetric  method  described  on  page  62, 
however,  is  more  rapid  and  convenient. 


74        Chemical  Analysis  of  Lead  and  Its  Compounds 

Silica 

Silica  is  found  to  be  present  in  oxides  of  lead 
both  as  free  silica  and  as  lead  silicate,  though 
usually  in  inappreciable  amounts. 

Digest  2  grams  of  the  sample  in  a  casserole 
with  2  grams  of  potassium  chlorate  and  15  c.c.  of 
dilute  nitric  acid.  Proceed  from  this  point  as  out- 
lined under  the  Analysis  of  Litharge,  page  88. 

Organic  Color 

The  adulteration  of  red  lead  and  orange  min- 
eral with  organic  coloring  matter  may  be  detected 
by  adding  20  c.c.  of  95  per  cent  alcohol  to  2  grams  of 
the  oxide,  heating  to  boiling  and  allowing  to;  settle. 
Pour  off  the  supernatant  liquid,  boil  with  water, 
allow  to  settle  and  add  a  very  small  amount  of 
ammonium  hydroxide.  If  either  the  alcohol,  water 
or  ammonium  hydroxide  are  colored,  it  indicates 
organic  coloring  matter.  The  quantitative  deter- 
mination is  exceedingly  difficult  and  the  organic 
color  is  usually  estimated  by  difference. 

U.  S.  Interdepartmental  Committee's  Recom- 
mended Laboratory  Examination  for 
Red  Lead,  Dry  and  Paste1 

1.  Laboratory  Examination,  Dry  Pigment 
(a)  Qualitative  Analysis 

Follow  ordinary  methods  of  qualitative  analysis. 
The  material  should  give  a  negative  test  for  matter 

1Prepared  and  recommended  by  the  U.  S.  Interdepartmental  Committee  on 
Paint  Specification  Standardization,  January  26,  1920.  P.  H.  Walker, 
Bureau  of  Standards,  Chairman  ;  H.  E.  Smith,  U.  S.  Railroad  Administra- 
tion, Secretary.  Circular  of  the  Bureau  of  Standards.  No.  90. 


Red  Lead  and  Orange  Mineral  75 

insoluble  in  a  mixture  of  nitric  acid  and  hydrogen 
peroxide,  and  material  other  than  oxides  of  lead. 
(If  more  than  a  faint  cloud  remains  after  treat- 
ment with  nitric  acid  and  hydrogen  peroxide,  it 
will  be  necessary  to  take  a  weighed  sample  and 
determine  the  percentage  of  this  insoluble  matter.) 
Boil  2  grams  of  the  sample  with  25  c.c.  of  95  per 
cent  ethyl  alcohol,  let  settle,  decant  off  the  super- 
natant liquid,  boil  the  residue  with  water,  decant 
as  before,  and  boil  the  residue  with  very  dilute 
ammonia.  If  the  alcohol,  water,  or  ammonia  are 
colored,  organic  coloring  matter  is  indicated,  which 
is  cause  for  rejection. 

(b)  True  Red  Lead 

Weigh  accurately  1  gram  of  the  sample  into  a 
200-c.c.  Erlenmeyer  flask,  add  a  few  drops  of  dis- 
tilled water,  and  rub  the  mixture  to  a  smooth  paste 
with  a  glass  rod  flattened  on  the  end.  Mix  in  a 
small  beaker  30  grams  of  pure  crystallized  sodium 
acetate,  2.4  grams  of  pure  potassium  iodide,  10  c.c. 
of  water,  and  10  c.c.  of  50  per  cent  acetic  acid. 
Stir  until  all  is  liquid,  warm  gently,  and,  if  neces- 
sary, add  2  to  3  c.c.  more  water.  Cool  to  room  tem- 
perature and  pour  into  the  flask  containing  the  red 
lead.  Rub  with  the  glass  rod  until  nearly  all  the 
red  lead  has  been  dissolved,  add  30  c.c.  of  water 
containing  5  to  6  grams  of  sodium  acetate,  and 
titrate  at  once  with  standard  sodium  thiosulphate 
solution,  adding  the  latter  rather  slowly  and  keep- 
ing the  liquid  constantly  in  motion  by  whirling 
the  flask.  When  the  solution  has  become  light  yel- 


76        Chemical  Analysis  of  Lead  and  Its  Compounds 

low,  rub  any  undissolved  particles  up  with  the  rod 
until  free  iodine  no  longer  forms,  wash  off  the 
rod,  and  add  the  sodium  thiosulphate  solution  until 
pale  yellow.  Add  starch  solution  and  titrate  until 
colorless,  add  standard  iodine  solution  until  the 
blue  color  is  just  restored.  From  the  amount  of 
standard  iodine  solution  used,  calculate  the  cor- 
rection to  be  applied  to  the  thiosulphate  reading, 
and  calculate  true  red  lead  (iodine  value  of  thio- 
sulphate X  2.7  =  =  Pb,04  value). 

(c)  Water  Soluble  Matter 

Digest  10  grams  of  the  sample  with  200  c.c.  of 
hot  water  on  a  steam  bath  for  1  hour;  filter  and 
wash  with  hot  water  until  no  residue  is  left  on 
evaporating  a  few  drops  of  the  washings.  Evap- 
orate the  filtrate  to  dryness  in  a  weighed  dish  on  a 
steam  bath,  heat  for  30  minutes  at  105  to  110°  C., 
cool,  and  weigh. 

(d)  Coarse  Particles 

Dry  a  standard  No.  200  brass  or  copper  sieve  in 
an  oven  at  105  to  110°  C.,  cool,  and  weigh  accu- 
rately. Weigh  50  grams  of  pigment  which  has 
been  previously  thoroughly  dried  by  heating  in  an 
oven  at  105  to  110°  C.  until  all  moisture  has  been 
driven  off.  Transfer  to  a  wide  mouth  bottle  or 
cylinder  of  about  300  c.c.  capacity,  add  about  200 
c.c.  of  dry  kerosene,  stopper,  and  shake  vigorously 
for  about  five  minutes.  Remove  the  stopper  and, 
with  a  jet  of  kerosene,  wash  back  into  the  cylin- 
der any  pigment  adhering  to  the  stopper.  Pour 
about  50  c.c.  of  the  kerosene  with  suspended  pig- 


Red  Lead  and  Orange  Mineral  77 

ment  onto  the  sieve,  let  drain  through,  and  grad- 
ually transfer  the  whole  of  the  kerosene  and  pig- 
ment to  the  sieve,  finally  using  a  jet  of  kerosene 
to  transfer  the  last  of  the  pigment.  With  proper 
manipulation  a  large  portion  of  the  pigment  will 
pass  through  the  sieve  during  the  process  of  trans- 
ferring from  the  cylinder.  When  all  pigment  has 
been  thrown  on  the  sieve,  wash  with  a  jet  of  kero- 
sene until  no  more  pigment  passes  through.  To 
make  sure  that  all  particles  have  been  thoroughly 
washed  through,  move  the  sieve  from  over  the 
vessel,  in  which  the  main  portion  of  kerosene  and 
pigment  has  been  caught,  to  over  a  clean  glass  dish 
resting  on  a  white  surface  and  wash  all  portions 
of  the  sieve  writh  a  jet  of  kerosene,  using  not  less 
than  200  c.c.  of  kerosene.  This  kerosene  caught 
in  this  dish  should  be  entirely  free  from  pigment. 
If  any  pigment  can  be  seen  in  the  liquid,  repeat  the 
washing  until  at  least  200  c.c.  can  be  washed 
through  without  showing  any  pigment.  Then  wash 
with  a  jet  of  kerosene  all  pigment  adhering  to  the 
frame  of  the  sieve  beneath  the  wire  mesh.  Finally, 
wash  the  kerosene  from  the  sieve  with  petroleum 
ether,  dry  the  sieve  at  105  to  110°  C.,  cool,  and 
weigh.  The  increase  in  weight  should  be  not  more 
than  0.150  gram. 

(e)  Running,  Streaking,  or  Sagging 

Mix  paint  and  apply  as  per  specifications.  About 
the  smallest  amount  that  can  be  conveniently  made 
up  will  be  154  grams  dry  red  lead,  40  c.c.  raw  lin- 
seed oil,  and  4  c.c.  each  of  turpentine  and  liquid 
drier. 


78        Chemical  Analysis  of  Lead  and  Its  Compounds 

2.  Laboratory  Examination,  Paste 

(a)  Caking  in  Container 

When  an  original  package  is  received  in  the  lab- 
oratory, it  shall  be  weighed,  opened,  and  stirred 
with  a  stiff  spatula  or  paddle.  The  paste  must  be 
no  more  difficult  to  break  up  and  show  no  more 
caking  than  a  normal  good  grade  of  red  lead  paste. 
The  paste  shall  finally  be  thoroughly  mixed,  re- 
moved from  the  container,  the  container  wiped 
clean,  and  weighed.  This  weight  subtracted  from 
the  weight  of  the  original  package  gives  the  net 
weight  of  the  contents.  A  portion  of  the  thor- 
oughly mixed  paste  shall  be  placed  in  a  clean  con- 
tainer and  the  portions  for  the  remaining  tests 
promptly  weighed  out. 

(b)  Mixing  with  Linseed  Oil,  Running,  Streaking, 
and  Sagging 

Mix  as  per  specification  to  a  paint,  first  using 
only  the  linseed  oil  and  noting  whether  the  paste 
breaks  up  readily  and  the  resulting  mixture  is 
smooth.  About  the  smallest  amount  that  can  be 
conveniently  made  up  will  be  154  grams  red  lead 
paste,  36  c.c.  raw  linseed  oil,  and  4  c.c.  each  of  tur- 
pentine and  liquid  drier. 

(c)  Moisture  and  Other  Volatile  Matter 

Weigh  accurately  from  3  to  5  grams  of  the  paste 
into  a  tared  flat  bottomed  dish,  about  5  cm.  in 
diameter,  spreading  the  paste  over  the  bottom. 
Heat  at  105  to  110°  C.  for  one  hour,  cool,  and 
weigh.  Calculate  the  loss  in  weight  as  percentage 
of  moisture  and  other  volatile  matter. 


Red  Lead  and  Orange  Mineral  79 

(d)  Percentage  of  Pigment 

Weigh  accurately  about  15  grams  of  the  paste 
into  a  weighed  centrifuge  tube.  Add  20  to  30  c.c. 
of  "extraction  mixture"  (see  reagents),  mix  thor- 
oughly with  a  glass  rod,  wash  the  rod  with  more 
of  the  extraction  mixture  and  add  sufficient  of  the 
reagent  to  make  a  total  of  60  c.c.  in  the  tube.  Place 
the  tube  in  the  container  of  a  centrifuge,  surround 
with  water,  and  counterbalance  the  container  of 
the  opposite  arm  with  a  similar  tube  or  a  tube  with 
water.  Whirl  at  a  moderate  speed  until  clear. 
Decant  the  clear  supernatant  liquid.  Repeat  the 
extraction  twice  with  40  c.c.  of  extraction  mixture, 
and  once  with  40  c.c.  of  ether.  After  drawing  off 
the  ether,  set  the  tube  in  a  beaker  of  water  at  about 
80°  C.  or  on  top  of  a  warm  oven  for  10  minutes, 
then  in  an  oven  at  110  to  115°  C.  for  2  hours.  Cool, 
weigh,  and  calculate  percentage  of  pigment. 

(e)  Examination  of  Pigment 

Grind  the  pigment  from  2  (d)  to  a  fine  powder, 
pass  through  a  No.  80  sieve  to  remove  any i  i  skins, ' ' 
preserve  in  a  stoppered  tube,  and  apply  tests  1  (a), 
1  (fc),  andl  (c). 

(f)  Preparation  of  Fatty  Acids 

To  about  25  grams  of  the  paste  in  a  porcelain 
casserole,  add  15  c.c.  of  aqueous  sodium  hydroxide 
(see  reagents),  and  75  c.c.  of  ethyl  alcohol,  mix  and 
heat  uncovered  on  a  steam  bath  until  saponification 
is  complete  (about  one  hour).  Add  100  c.c.  of 
water,  boil,  add  an  excess  of  sulphuric  acid  of  spe- 
cific gravity  1.2  (8  to  10  c.c.  will  usually  suffice), 


80         Chemical  Analysis  of  Lead  and  Its  Compounds 

boil,  stir,  and  transfer  to  a  separatory  funnel  to 
which  some  water  has  been  previously  added. 
Draw  off  as  much  as  possible  of  the  acid  aqueous 
layer  and  lead  sulphate  precipitate,  wash  once  with 
water;  then  add  50  c.c.  water  and  50  c.c.  ether. 
Shake  very  gently  with  a  whirling  motion  to  dis- 
solve the  fatty  acids  in  the  ether,  but  not  violently, 
so  as  to  avoid  forming  an  emulsion.  Draw  off  the 
aqueous  layer  and  wash  the,  ether  layer  with  one 
15  c.c.  portion  of  water  and  then  with  5  c.c.  por- 
tions of  water  until  free  from  sulphuric  acid.  Then 
draw  off  the  water  layer  completely.  Transfer  the 
ether  solution  to  a  dry  flask,  add  25  to  50  grams  of 
anhydrous  sodium  sulphate.  Stopper  the  flask  and 
let  stand  with  occasional  shaking  at  a  tempera- 
ture below  25°  C.  until  the  water  is  completely  re- 
moved from  the  ether  solution,  which  will  be  shown 
by  the  solution  becoming  perfectly  clear  above  the 
solid  sodium  sulphate.  Decant  this  clear  solution 
(if  necessary  through  a  dry  filter  paper)  into  a  dry 
100-c.c.  Erlenmeyer  flask.  Pass  a  rapid  current  of 
dry  air  (pass  through  CaCL  tower)  into  the  mouth 
of  the  Erlenmeyer  flask  and  heat  to  a  temperature 
below  75°  C.  on  a  dry  hot  plate  until  the  ether  is 
entirely  driven  off.  The  fatty  acids  prepared  as 
above  should  be  kept  in  a  stoppered  flask  and  exam- 
ined at  once. 

Note. — It  is  important  to  follow  all  of  the  details,  since  ether  generally 
contains  alcohol,  and  after  washing  with  water  always  contains  water. 
It  is  very  difficult  to  remove  water  and  alcohol  by  evaporation  from  fatty 
acids,  but  the  washing  of  the  ether  solution  and  subsequent  drying  with 
anhydrous  sodium  sulphate  removes  both  water  and  alcohol.  Ether,  in  the 
absence  of  water  and  alcohol,  is  easily  removed  from  fatty  acids  by  gentle 
heat. 


Red  Lead  and  Orange  Mineral  81 

(g)  Test  for  Mineral  Oil 

Place  10  drops  of  the  fatty  acid  (/)  in  a  50-c.c. 
test  tube,  add  5  c.c.  of  alcoholic  soda  (see  re- 
agents), boil  vigorously  for  five  minutes,  add  40 
c.c.  of  water,  and  mix;  a  clear  solution  indicates 
that  not  more  than  traces  of  unsaponifiable  matter 
are  present.  If  the  solution  is  not  clear,  the  oil  is 
not  pure  linseed  oil. 

(h)  Iodine  Number  of  Fatty  Acids 

Place  a  small  quantity  of  the  fatty  acids  (/)  in 
a  small  weighing  burette  or  beaker.  Weigh  accu- 
rately. Transfer  by  dropping  about  0.15  gram 
(0.10  to  0.20  gram)  to  a  500-c.c.  bottle  having  a 
well  ground  glass  stopper,  or  an  Erlenmeyer  flask 
having  a  specially  flanged  neck  for  the  iodine  test. 
Reweigh  the  burette  or  beaker  and  determine  the 
amount  of  sample  used.  Add  10  c.c.  of  chloroform. 
Whirl  the  bottle  to  dissolve  the  sample.  Add  10 
c.c.  of  chloroform  to  two  empty  bottles  like  that 
used  for  sample.  Add  to  each  bottle  25  c.c.  of  the 
Hanus  solution  (see  reagents)  and  let  stand  with 
occasional  shaking  for  one-half  hour.  Add  10  c.c. 
of  the  15  per  cent  potassium  iodide  solution  and 
100  c.c.  of  water,  and  titrate  with  standard  sodium 
thiosulphate,  using  starch  as  indicator.  The  titra- 
tions  on  the  two  blank  tests  should  agree  within 
0.1  c.c.  From  the  difference  between  the  average 
of  the  blank  titrations  and  the  titration  on  the  sam- 
ple and  the  iodine  value  of  the  thiosulphate  solu- 
tion, calculate  the  iodine  number  of  the  sample 
tested.  (Iodine  number  is  centigrams  of  iodine  to 


82         Chemical  Analysis  of  Lead  and  Its  Compounds 

1  gram  of  sample.)  If  the  iodine  number  is  less 
than  170,  the  oil  does  not  meet  the  specification. 

(i)  Coarse  Particles  and  "Skins" 

Weigh  an  amount  of  paste  containing  50  grams 
of  pigment  (see  2  (d)),  add  200  c.c.  of  kerosene, 
and  wash  through  a  No.  200  sieve  as  in  1  (d).  The 
residue  remaining  in  the  sieve  shall  not  be  more 
than  0.25  gram. 

3.     Reagents 

(a)  Extraction  Mixture 

10  volumes  ether  (ethyl  ether). 
6  volumes  benzol. 
4  volumes  methyl  alcohol. 
1  volume  acetone. 

(b)  Aqueous  Sodium  Hydroxide 

Dissolve  100  grams  of  sodium  hydroxide  in  dis- 
tilled water  and  dilute  to  300  c.c. 

(c)  Standard  Sodium  Thiosulphate  Solution 
Dissolve  pure  sodium  thiosulphate  in  distilled 

water  that  has  been  well  boiled  to  free  it  from  car- 
bon dioxide,  in  the  proportion  of  24.83  grams  of 
crystallized  sodium  thiosulphate  to  1000  c.c.  of  the 
solution.  It  is  best  to  let  this  solution  stand  for 
about  two  weeks  before  standardizing.  Standard- 
ardize  with  pure  resublimed  iodine.  (See  Tread- 
well-Hall,  Analytical  Chemistry,  Vol.  II,  3d  ed., 
p.  646.)  This  solution  will  be  approximately  deci- 
normal  and  it  is  best  to  leave  it  as  it  is  after  deter- 
mining its  exact  iodine  value,  rather  than  to 


Red  Lead  and  Orange  Mineral  83 

attempt  to  adjust  it  to  exactly  decinormal.  Pre- 
serve in  a  stock  bottle  provided  with  a  guard  tube 
filled  with  soda  lime. 

(d)  Starch  Solution 

Stir  up  2  to  3  grams  of  potato  starch  or  5  grams 
of  soluble  starch  with  100  c.c.  of  1  per  cent  sali- 
cylic acid  solution,  add  300  to  400  c.c.  of  boiling 
water,  and  boil  the  mixture  until  the  starch  is  prac- 
tically dissolved,  then  dilute  to  1  liter. 

(e)  Standard  Iodine  Solution 

Dissolve  13  grams  of  resublimed  iodine  and  18 
grams  of  pure  potassium  iodide  (free  from 
iodates)  in  50  c.c.  of  distilled  water,  and  dilute  to 
1000  c.c.  Determine  its  exact  value  by  titrating 
with  the  standard  sodium  thiosulphate  solution. 

(f)  Potassium  Iodide  Solution 

Dissolve  150  grams  of  potassium  iodide,  free 
from  iodate,  in  distilled  water  and  dilute  to 
1000  c.c. 

(g)  Hanus  Solution 

Dissolve  13.2  grams  of  iodine  in  1000  c.c.  of 
99.5  per  cent  glacial  acetic  acid,  which  will  not 
reduce  chromic  acid.  Add  enough  bromine  to 
double  the  halogen  content,  determined  by  titration 
(3  c.c.  of  bromine  is  about  the  proper  amount). 
The  iodine  may  be  dissolved  by  the  aid  of  heat,  but 
the  solution  should  be  cold  when  the  bromine  is 
added, 


84         Chemical  Analysis  of  Lead  and  Its  Compounds 

(h)  Alcoholic  Sodium  Hydroxide  Solution 

Dissolve  pure  sodium  hydroxide  in  95  per  cent 
ethyl  alcohol  in  the  proportion  of  about  22  grams 
per  1000  c.c.  Let  stand  in  a  stoppered  bottle.  De- 
cant the  clear  liquid  into  another  bottle  and  keep 
well  stoppered.  This  solution  should  be  colorless 
or  only  slightly  yellow  when  used,  and  it  will  keep 
colorless  longer  if  the  alcohol  is  previously  treated 
with  sodium  hydroxide  (about  80  grams  to  1000 
c.c.),  kept  at  about  50°  C.  for  15  days,  and  then 
distilled. 


CHAPTER  IX 

/ 

LITHARGE 

Litharge,  the  monoxide  of  lead,  PbO,  may  con- 
tain small  percentages  of  iron,  copper,  silica,  silver 
and  free  metallic  lead.  When  the  litharge  has  been 
made  by  a  process  where  steam  is  used,  there  may 
be  an  appreciable  amount  of  moisture  present.  It 
appears  on  the  market  in  two  colors,  yellow  and 
red.  In  some  instances  litharge  is  found  contain- 
ing a  comparatively  large  percentage  of  red  lead, 
which  in  certain  uses  is  undesirable.  The  deter- 
mination of  each  of  the  foreign  constituents  in 
litharge  depends  largely  upon  the  use  to  which  the 
litharge  is  to  be  put,  as  in  very  few  cases  are  all 
the  constituents  determined. 

Analysis 
Moisture 

Dry  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Free  Metallic  Lead 

Two  grams  of  the  sample  are  treated  in  a  beaker 
with  hot  water  and  just  sufficient  acetic  acid  is 
slowly  added,  to  dissolve  the  lead  oxide.  Stir  the 
solution  well  and  note  whether  any  lead  silicate 
remains  undissolved.  Should  such  remain,  con- 
tinue stirring  until  solution  has  been  effected.  The 

85 


86        Chemical  Analysis  of  Lead  and  Its  Compounds 

solution  should  never  have  greater  than  a  5  per 
cent  acetic  acid  strength. 

Filter  the  solution  and  wash  the  residual  metal 
three  or  four  times  by  decantation  with  hot  water, 
having  all  the  wash  water  pass  through  the  filter 
paper,  which  is  finally  thoroughly  washed  with  hot 
water.  Transfer  any  metal  on  the  filter  paper  to 
the  beaker  containing  the  residual  lead,  add  1  c.c. 
of  concentrated  nitric  acid  and  heat  to  solution. 
Dilute  with  50  c.c.  of  water,  add  1  gram  of  sodium 
acetate  and  follow  this  with  an  excess  of  saturated 
neutral  potassium  bichromate  solution,  sufficient 
to  precipitate  all  the  lead.  Boil,  dilute  to  100  c.c., 
allow  to  cool,  filter  off  the  lead  chromate,  wash 
thoroughly  and  determine  the  lead  chromate  gravi- 
metrically  by  drying  at  100°  C.  or  volumetrically 
by  titration  of  the  chromic  acid  present  as  outlined 
under  the  Analysis  of  Lead  Ores.  The  factor  for 
the  direct  determination  of  lead  is,  however,  in  this 
case  0.5,  as  a  2  gram  sample  is  used. 

Red  Lead 

Determine  the  percentage  of  red  lead  present 
as  outlined  under  the  Analysis  of  Red  Lead. 

Iron 

Treat  1  gram  of  the  sample  with  10  c.c.  of  water 
and  just  sufficient  nitric  acid,  added  drop  by  drop, 
to  cause  complete  solution.  Heat  to  boiling  to  oxi- 
dize all  the  iron  and  determine  it  colorimetrically 
as  outlined  on  page  62. 


Litharge  87 

Copper 

Copper  may  be  rapidly  and  accurately  deter- 
mined by  the  method  described  on  page  60.  The 
following  gravimetric  method,  however,  may  be 
found  more  convenient  if  only  a  few  determinations 
are  to  be  made. 

Twenty  grams  of  the  litharge  contained  in  a  200- 
c.c.  flask  are  dissolved  in  nitric  acid  (50  c.c.  concen- 
trated nitric  acid  to  100  c.c.  water).  Boil  to  com- 
plete solution.  Add  40  c.c.  of  dilute  sulphuric 
acid  (1:1),  boil  gently  for  one  hour  and  allow  to 
cool.  Filter  off  the  lead  sulphate  and  wash  the 
precipitate  thoroughly.  Nearly  neutralize  all  the 
free  acid  present  with  ammonium  hydroxide, 
render  slightly  acid  with  hydrochloric  acid,  warm 
the  solution  and  pass  in  hydrogen  sulphide  until 
no  further  precipitation  of  sulphide  occurs.  Filter 
off  the  precipitate  without  washing,  using  some  of 
the  filtrate  to  transfer  the  last  traces  of  sulphide 
to  the  filter  paper.  Dissolve  the  precipitate  in  a 
little  nitric  acid  and  wash  the  filter  paper  thor- 
oughly with  hot  water.  Add  3  c.c.  of  concentrated 
sulphuric  acid,  evaporate  until  the  white  fumes  of 
sulphuric  acid  are  evolved  and  allow  the  solution  to 
cool.  Add  a  little  water  and  allow  to  stand  for 
some  hours.  Filter  off  the  lead  sulphate,  washing 
with  hot  water  containing  a  little  sulphuric  acid. 

Heat  the  filtrate  to  boiling  and  precipitate  the 
copper  as  sulphide  with  hydrogen  sulphide  in  an 
ammoniacal  solution.  Filter  off  the  copper  sulphide 
through  an  ashless  filter  paper,  wash,  ignite  and 


88         Chemical  Analysis  of  Lead  and  Its  Compounds 

weigh  in  a  covered  porcelain  crucible,  from  which 
the  heat  and  cover  are  occasionally  removed  for 
a  few  seconds. 

The  precipitate  will  consist  of  a  mixture  of  CuO 
and  Cu2S.  Since  the  percentage  of  copper  is  the 
same  in  both  of  these,  the  copper  may  be  deter- 
mined by  multiplying  the  amount  found  by  the 
factor  0.7988. 

Silica 

Digest  5  grams  of  the  sample  in  a  covered 
casserole  with  2  grams  of  potassium  chlorate  and 
15  c.c.  of  dilute  nitric  acid  (1:1).  Evaporate  to 
dryness  and  dehydrate.  Treat  the  residue,  after 
cooling,  with  hot  water  and  nitric  acid.  Heat  to 
boiling,  and  filter  the  solution  through  an  ashless 
filter  paper.  Wash  the  residue  and  filter  paper 
thoroughly  with  hot  acid  ammonium  acetate  solu- 
tion, made  up  to  a  strength  as  outlined  under  the 
Analysis  of  Lead  Ores.  Should  the  residue  show  a 
trace  of  iron,  wash  it  thoroughly  with  dilute  hy- 
drochloric acid.  Complete  the  washing  with  hot 
water,  dry,  ignite  and  weigh  as  SiO..  The  residue 
may  be  volatilized  with  hydrofluoric  acid,  if  there 
is  any  doubt  regarding  the  purity  of  the  silica. 

The  silica  is  present  as  lead  silicate  and  free 
silica.  The  above  method  determines  the  total 
content  of  silica.  The  free  silica  may  be  deter- 
mined by  dissolving  the  litharge  in  dilute  nitric 
acid.  Heat  to  boiling,  filter,  wash,  ignite  and  weigh 
as  silica. 


CHAPTER    X 

BASIC  CARBONATE  OF  LEAD 

(Corroded  White  Lead) 

Basic  carbonate  white  lead  (2PbCO:!.Pb(OH)2) 
contains  approximately  80  per  cent  metallic  lead 
and  20  per  cent  carbonic  acid  and  combined  water, 
with  traces  of  silver,  antimony,  lead,  and  other 
metals.  The  analysis  of  basic  carbonate  white  lead 
can  best  be  carried  out  by  Walker 's  method.1 

Analysis 
Total  Lead 

"  Weigh  1  gram  of  the  sample,  moisten  with 
water,  dissolve  in  acetic  acid,  filter,  wash,  ignite, 
and  weigh  the  insoluble  impurities.  To  the  filtrate 
from  the  insoluble  matter  add  25  c.c.  of  sulphuric 
acid  (1:1),  evaporate  and  heat  until  the  acetic  acid 
is  driven  off ;  cool,  dilute  to  200  c.c.  with  water,  add 
20  c.c.  of  ethyl  alcohol,  allow  to  stand  for  two  hours, 
filter  on  a  Grooch  crucible,  wash  with  1  per  cent 
sulphuric  acid,  ignite,  and  weigh  as  lead  sulphate. 
Calculate  to  total  lead  (PbS04  X  0.68292  =  Pb)  or 
calculate  to  basic  carbonate  of  lead  (white  lead)  by 
multiplying  the  weight  of  lead  sulphate  by  0.85258. 

' i  The  filtrate  from  the  lead  sulphate  may  be  used 
to  test  for  other  metals,  though  white  lead  is  only 
rarely  adulterated  with  soluble  substances;  test, 

iP.  H.  Walker,  Bureau  of  Chemistry  Bulletin  No.  109,  revised, 
U.  S.  Dept.  of  Agriculture,  pp.  21  and  22. 

89 


90        Chemical  Analysis  of  Lead  and  Its  Compounds 

however,  for  zinc,  which  may  be  present  as  zinc 
oxide. 

"Instead  of  determining  the  total  lead  as  sul- 
phate it  may  be  determined  as  lead  chromate  by 
precipitating  the  hot  acetic  acid  solution  with  potas- 
sium bichromate,  filtering  on  a  Gooch  crucible, 
igniting  at  a  low  temperature,  and  weighing  as  lead 

chromate. 

Complete  Analysis 

"When  it  is  necessary  to  determine  the  exact 
composition  of  a  pure  white  lead,  heat  1  gram  of 
the  pigment  in  a  porcelain  boat  in  a  current  of 
dry,  carbon  dioxide  free  air,  catching  the  water  in 
sulphuric  acid  and  calcium  chloride  and  the  car- 
bon dioxide  in  soda  lime  or  potassium  hydroxide 
(1.27  specific  gravity).  By  weighing  the  residue 
of  lead  monoxide  in  the  boat  all  the  factors  for 
determining  the  total  composition  are  obtained. 
Figure  the  carbon  dioxide  to  lead  carbonate 
(PbCO;t),  calculate  the  lead  monoxide  correspond- 
ing to  the  lead  carbonate  (PbCO.,)  and  subtract 
from  the  total  lead  monoxide,  calculate  the  remain- 
ing lead  monoxide  to  lead  hydroxide  (Pb(OH)2), 
calculate  the  water  corresponding  to  lead  hydrox- 
ide and  subtract  from  the  total  water,  the 
remainder  being  figured  as  moisture. 

"This  method  assumes  the  absence  of  acetic  acid. 
Thompson1  states  that  acetic  acid  varies  from  0.05 
per  cent  in  Dutch  process  white  lead  to  0.7  per  cent 
in  some  precipitated  white  leads.  It  is  then  more 
accurate  to  determine  the  carbon  dioxide  by  evolu- 

ij.  Soc.  Chem.  Ind.,  1905,  24:487. 


Basic  Carbonate  of  Lead  91 

tion ;  this  is  especially  the  case  when  working  with 
a  lead  extracted  from  an  oil  paste,  as  the  lead  soap 
and  unextr acted  oil  will  cause  a  considerable  error 
by  the  ignition  method.  In  determining  carbon 
dioxide  by  the  evolution  method,  liberate  the  carbon 
dioxide  with  dilute  nitric  acid,  have  a  reflux  con- 
denser next  to  the  evolution  flask  and  dry  the  car- 
bon dioxide  with  calcium  chloride  before  absorbing 
it  in  the  potassium  hydroxide  bulbs. 

Acetic  Acid 

"It  is  sometimes  necessary  to  determine  acetic 
acid.  Thompson's  method1  is  as  follows: 

"Eighteen  grams  of  the  dry  white  lead  are 
placed  in  a  500-c.c.  flask,  this  flask  being  arranged 
for  connection  with  a  steam  supply  and  also  with 
an  ordinary  Liebig  condenser.  To  this  white  lead 
is  added  40  c.c.  of  syrupy  phosphoric  acid,  18  grams 
of  zinc  dust,  and  about  50  c.c.  of  water.  The  flask 
containing  the  material  is  heated  directly  and  dis- 
tilled down  to  a  small  bulk.  Then  the  steam  is 
passed  into  the  flask  until  it  becomes  about  half 
full  of  condensed  water,  when  the  steam  is  shut 
off  and  the  original  flask  heated  directly  and  dis- 
tilled down  to  the  same  small  bulk — this  operation 
being  conducted  twice.  The  distillate  is  then 
transferred  to  a  special  flask  and  1  c.c.  of  syrupy 
phosphoric  acid  added  to  insure  a  slightly  acid 
condition.  The  flask  is  then  heated  and  distilled 
down  to  a  small  bulk — say,  20  c.c.  Steam  is  then 
passed  through  the  flask  until  it  contains  about  200 

ij.  Soc.  Chem.  Ind.,  1905,  24:487. 


92        Chemical  Analysis  of  Lead  and  Its  Compounds 

c.c.  of  condensed  water,  when  the  steam  is  shut  off 
and  the  flask  heated  directly.  These  operations  of 
direct  distillation  and  steam  distillation  are  con- 
ducted until  10  c.c.  of  the  distillate  require  but  a 
drop  of  tenth  normal  alkali  to  produce  a  change 
in  the  presence  of  phenolphthalein.  Then  the  bulk 
of  the  distillate  is  titrated  with  tenth  normal  sodi- 
um hydroxide,  and  the  acetic  acid  calculated.  It 
will  be  found  very  convenient  in  this  titration, 
which  amounts  in  some  cases  to  600-700  c.c.,  to  ti- 
trate the  distillate  when  it  reaches  200  c.c.,  and  so 
continue  titrating  every  200  c.c.  as  it  distills  over. 

4 'If  the  white  lead  contains  appreciable  amounts 
of  chlorine  it  is  well  to  add  some  silver  phosphate 
to  the  second  distillation  flask  and  not  carry  the 
distillation  from  this  flask  too  far  at  any  time. 

4 'The  method  used  by  the  chemists  of  the  Navy 
Department  is  as  follows:  Weigh  25  grams  of 
white  lead  in  an  Erlenmeyer  flask,  add  75  c.c.  of 
25  per  cent  phosphoric  acid,  distill  with  steam  to 
a  500  c.c.  distillate,  add  to  the  distillate  some  milk 
of  barium  carbonate,  bring  to  a  boil,  filter,  keeping 
the  solution  at  the  boiling  point  (it  is  not  necessary 
to  wash),  add  an  excess  of  sulphuric  acid  to  the  fil- 
trate and  determine  the  barium  sulphate  in  the 
usual  manner;  subtract  53  milligrams  from  the 
weight  of  the  barium  sulphate  and  calculate  the  re- 
mainder as  acetic  acid  (BaS04  times  0.515  equals 
CH3COOH).  The  object  of  this  rather  indirect 
method  is  to  avoid  any  error  that  might  arise  from 
fatty  acids  being  carried  over  by  the  steam  distilla - 


Basic  Carbonate  of  Lead 


FIG.  2.     Carbon  Dioxide  Apparatus. 


94        Chemical  Analysis  of  Lead  and  Its  Compounds 

tion.    For  white  lead  that  has  not  been  ground  in 
oil,  Thompson 's  method  is  to  be  preferred. ' ' 

Carbonic  Acid 

The  carbonic  acid  content  of  white  lead  may  be 
determined  by  using  the  Scheibler  apparatus,  com- 
plete reference  to  which,  with  all  tables,  may  be 
found  in  "The  Analysis  of  Paints  and  Painting 
Materials,  'n  page  6.  A  more  simple  and  efficacious 
method  of  determining  the  carbonic  acid  content 
will  be  found  in  the  following  method. 

The  method  can  be  used  in  such  cases  where  the 
substances  to  be  analyzed  evolve  gases  other  than 
carbon  dioxide;  that  is,  hydrogen  sulphide,  sul- 
phur dioxide,  or  organic  matter.  The  appa- 
ratus used  is  shown  in  Fig.  2.  A  weighed  sample 
of  the  substance  is  introduced  into  the  Erlen- 
meyer  flask  (A).  Into  flask  (B)  is  placed  a  10 
per  cent  solution  of  barium  chloride,  more  than 
sufficient  to  hold  the  carbon  dioxide  evolved,  and 
20  c.c.  of  concentrated  ammonium  hydroxide  free 
from  carbon  dioxide.  If  sulphides  are  present, 
it  is  sometimes  advisable  to  pass  the  liberated  gas 
first  through  a  few  c.c.  of  strong  potassium  per- 
manganate. The  flask  (B)  is  warmed  until  com- 
pletely filled  with  ammonia  fumes.  Flask  (D)  is 
a  safety  bottle  containing  the  same  solution  as 
flask  (B).  Only  in  rare  cases  will  any  trace  of  the 
carbon  dioxide  be  noticed  in  the  safety  flask.  After 
flask  (B)  is  completely  filled  with  ammonia  vapor, 

iThe  Analysis  of  Paints  and  Painting  Materials,  Gardner  and 
§chaeffer:     The  McGraw-Hill  Book  Company,  New  York, 


Basic  Carbonate  of  Lead  95 

make  all  connections  and  allow  the  hydrochloric 
acid  to  drop  slowly  from  the  separatory  funnel  into 
the  decomposition  flask  (A).  When  effervescence 
has  ceased,  heat  the  contents  of  the  flask  until  filled 
with  steam.  The  delivery  tubes  and  sides  of  the 
precipitating  flask  are  then  washed  with  boiling- 
water,  the  flask  is  filled  to  the  neck,  stoppered,  and 
the  precipitated  barium  carbonate  allowed  to  set- 
tle. Wash  thoroughly  by  decantation,  each  time 
stoppering  the  flask  to  prevent  any  error  from  the 
carbon  dioxide  present  in  the  air,  and  determine 
either  gravimetrically,  by  conversion  into  barium 
sulphate,  or  volumetrically,  by  dissolving  in  stand- 
ard hydrochloric  acid  and  titrating  the  excess  of 
acid  used  with  standard  potassium  hydroxide.  Cal- 
culate the  barium  found  to  carbonate  and  the 
amount  of  carbon  dioxide  from  the  found  carbon- 
ate. The  entire  operation  may  be  hastened  by  con- 
ducting a  brisk  current  of  air  free  from  carbon 
dioxide  through  the  entire  apparatus. 

Two  rapid  volumetric  methods  for  the  determi- 
nation of  carbonic  acid  contents  are  described  in 
detail  by  Leon  T.  Bonser  in  the  Journal  of  Indus- 
trial and  Chemical  Engineering,  March,  1912,  page 
203,  and  by  H.  W.  Brubaker  in  the  same  journal, 
August,  1912. 

A  few  typical  analyses  of  basic  carbonate  white 
lead,  for  impurities,  are  given  in  the  table  on  the 
following  page. 


96         Chemical  Analysis  of  Lead  and  Its  Compounds 


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O  O    O  O 

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Basic  Carbonate  of  Lead 


97 


U.  S.  Interdepartmental  Committee's  Recom- 
mended Specification  for  Basic  Carbon- 
ate White  Lead,  Dry  and  Paste1 

1.  General 

Basic  carbonate  white  lead  may  be  ordered  in 
the  form  of  dry  pigment  or  paste  ground  in  lin- 
seed oil.  Material  shall  be  purchased  by  net  weight. 

(a)  Dry  Pigment 

The  pigment  shall  be  the  product  made  from 
metallic  lead  and  shall  have  a  composition 
corresponding  approximately  to  the  formula 
2PbC03.Pb(OH)2.  It  shall  be  thoroughly  washed 
after  corroding,  shall  be  free  from  impurities  and 
adulterants,  and  shall  meet  the  following  require- 
ments : 

Color  —  Color  Strength 

When  specified,  shall  be  equal  to  that  of  a  sam- 
ple mutually  agreed  upon  by  buyer  and  seller. 


Minimum 

Maximum 

Coarse  particles: 
Retained  on  Standard  No    2002  screen 

Per  cent 

Per  cent 

None 

Retained  on  Standard  No   3252  screen   . 

20 

Lead  carbonate   

65.0 

75.0 

Total  impurities    including  moisture 

2  0 

1Prepared  and  recommended  by  the  U.  S.  Interdepartmental  Committee  on 
Paint  Specification  Standardization  August  11,  1919.  P.  H.  Walker,  Bureau 
of  Standards,  Chairman  ;  H.  E.  Smith,  U.  S.  Railroad  Administration, 
Secretary.  Circular  of  the  Bureau  of  Standards.  No.  84. 

-The  No.  200  and  No.  325  screens  are  the  same  as  screens  formerly  known 
as  200-mesh  and  350-mesh. 


98         Chemical  Analysis  of  Lead  and  Its  Compounds 

(b)  Paste 

The  paste  shall  be  made  by  thoroughly  grinding 
the  above  described  pigment  with  pure  raw  or 
refined  linseed  oil. 

The  paste  as  received  shall  not  be  caked  in  the 
container  and  shall  break  up  readily  in  oil  to  form 
a  smooth  paint  of  brushing  consistency.  The  paste 
shall  consist  of : 


Minimum 

Maximum 

Per  cent 
90 

Per  cent 
92 

Linseed  oil        

8 

10 

Moisture  and  other  volatile  matter 

0  7 

Coarse  particles  and  "skins"'  (total  residue  re- 
tained on  ^o  3^5  screen  based  on  pigment) 

2  0 

2.  Sampling 

It  is  mutually  agreed  by  buyer  and  seller  that  a 
single  package  out  of  each  lot  of  not  more  than 
1000  packages  be  taken  as  representative  of  the 
whole. 

With  the  dry  pigment,  this  package  shall  be 
opened  by  the  inspector  and  a  sample  of  not  less 
than  5  pounds  taken  at  random  from  the  contents 
and  sent  to  the  laboratory  for  test.  When  re- 
quested, a  duplicate  sample  may  be  taken  from  the 
same  package  and  delivered  to  the  seller,  and  the 
inspector  may  take  a  third  sample  to  hold  for  test 
in  case  of  dispute. 

Whenever  possible,  an  original  unopened  con- 
tainer shall  be  sent  to  the  laboratory  with  the 


Basic  Carbonate  of  Lead  99 

paste ;  and  when  this  is  for  any  reason  not  done, 
the  inspector  shall  determine  by  testing  thor- 
oughly with  a  paddle  or  spatula  whether  the  mate- 
rial meets  the  requirement  regarding  not  caking 
in  the  container.  (See  4  (a).)  After  assuring 
himself  that  the  paste  is  not  caked,  the  inspector 
shall  draw  a  sample  of  not  less  than  5  pounds  of 
the  thoroughly  mixed  paste,  place  it  in  a  clean  dry 
metal  or  glass  container,  which  must  be  filled  with 
the  sample,  closed  with  a  tight  cover,  sealed, 
marked,  and  sent  to  the  laboratory  for  test  with 
the  inspector's  report  on  caking  in  container. 

Samples  will  in  general  be  tested  by  the  follow- 
ing methods,  but  the  purchaser  reserves  the  right 
to  apply  any  additional  tests,  or  use  any  available 
information  to  ascertain  whether  the  material 
meets  the  specification. 

3.  Laboratory  Examination  of  Dry  Pigment 

(a)  Color 

Take  1  gram  of  the  sample,  add  10  to  12  drops 
linseed  oil,  rub  up  on  a  stone  slab  or  glass  plate 
with  a  flat  bottomed  glass  or  stone  pestle  or  muller 
to  a  uniform  smooth  paste.  Treat  in  a  similar  man- 
ner 1  gram  of  the  standard  basic  carbonate  white 
lead.  Spread  the  two  pastes  side  by  side  on  a  glass 
microscope  slide  and  compare  the  colors.  If  the 
sample  is  as  white  or  whiter  than  the  "  standard, " 
it  passes  this  test.  If  the  standard  is  whiter  than 
the  sample,  the  material  does  not  meet  the  speci- 
fication. 


100       Chemical  Analysis  of  Lead  and  Its  Compounds 

(b)  Color  Strength 

Weigh  accurately  0.01  gram  of  lampblack,  place 
on  a  large  glass  plate  or  stone  slab,  add  5  drops 
of  linseed  oil,  and  rub  up  with  a  flat  bottomed  glass 
pestle,  or  muller,  then  add  exactly  10  grams  of 
the  sample  and  45  drops  of  linseed  oil,  and  grind 
with  a  circular  motion  of  the  muller  50  times; 
gather  up  with  a  sharp  edged  spatula  and  grind  out 
two  more  times  in  a  like  manner,  giving  the  pestle 
a  uniform  pressure.  Treat  another  0.01  gram  of 
the  same  lampblack  in  the  same  manner,  except 
that  10  grams  of  standard  basic  carbonate  white 
lead  is  used  instead  of  the  10  grams  of  the  sample. 
Spread  the  two  pastes  side  by  side  on  a  glass 
microscope  slide  and  compare  the  colors.  If  the 
sample  is  as  light  or  lighter  in  color  than  the  stand- 
ard, it  passes  this  test.  If  the  standard  is  lighter 
in  color  than  the  sample,  the  material  does  not  meet 
the  specification. 

(c)  Coarse  Particles 

Dry  in  an  oven  at  105°  to  110°  C.  a  No.  200  and  a 
No.  325  sieve,  cool  and  weigh  accurately.  Weigh  100 
grams  of  the  sample ;  dry  at  100°  C.,  transfer  to 
a  mortar,  add  100  c.c.  kerosene,  thoroughly  mix  by 
gentle  pressure  with  a  pestle  to  break  up  all  lumps, 
wash  with  kerosene  first  through  the  200  and  then 
through  the  325  sieve,  breaking  up  all  lumps,  but 
not  grinding.  After  washing  with  kerosene  until 
all  but  the  particles  which  are  too  coarse  to  pass 
the  sieves  have  been  washed  through,  wash  all 
kerosene  from  the  sieves  with  ether  or  petroleum 
ether,  heat  the  sieves  for  one  hour  at  105  to  110° 


Basic  Carbonate  of  Lead  101 

C.,  cool  and  weigh.  The  increase  in  weight  of  the 
200  sieve  should  be  not  more  than  0.020  gram  and 
of  the  325  sieve  not  more/th^n  2.QOO  grams. 

(d)  Qualitative  Analysis   '  aj> 

Test  for  matter  insoJ^Vle  hi  acetic  acid,  zinc,  cal- 
cium, etc.,  by  the  regular  methods  of  qualitative 
analysis. 

(e)  Moisture 

Place  1  gram  of  the  sample  in  a  tared  wide 
mouth  short  weighing  tube  provided  with  a  glass 
stopper.  Heat  with  stopper  removed  for  two  hours 
at  a  temperature  between  100  and  105°  C.  Insert 
stopper,  cool  and  weigh.  Calculate  loss  in  weight 
as  moisture. 

(f)  Total  Lead  and.  Insoluble  Impurity 

Weigh  1  gram  of  the  sample,  moisten  with  water, 
dissolve  in  acetic  acid.  If  any  insoluble  residue 
remains,  filter,  dry  at  105  to  110°  C.  and  weigh  as 
insoluble  impurity.  Dilute  the  solution  to  about 
200  c.c.,  make  alkaline  with  NH4OH,  then  acid  with 
acetic  acid,  heat  to  boiling  and  add  10  to  15  c.c.  of 
a  10  per  cent  solution  of  sodium  bichromate  or 
potassium  bichromate,  and  heat  until  the  yellow 
precipitate  assumes  an  orange  color.  Let  it  settle 
and  filter  on  a  Gooch  crucible,  washing  by  decan- 
tation  with  hot  water  until  the  washings  are  color- 
less, and  finally  transferring  all  the  precipitate. 
Then  wash  with  95  per  cent  ethyl  alcohol  and  then 
with  ethyl  ether;  dry  at  100°  C.  and  weigh 
PbCr04.  Calculate  to  lead  oxide  (PbCrO,  X  0.69 


102       Chemical  Analysis  oj  Lead  and  Its  Compounds 

•-  PbO).  Total  lead  may  be  determined  by  the 
sulphate  method  if  preferred. 

(g)  Carbon-* Dioxide 

Determine  by  evolution  with  dilute  acid  and  ab- 
sorption  iri'sSda^ime  or'KQH  solution,  calculate 
C02  to  PbCbV  subtract  PbO  equivalent  from  total 
PbO  and  calculate  residual  PbO  to  Pb(OH)2. 

CO,  X  6.072  =  PbCO, 

CO.  X  5.072  =  PbO 

PbO  X  1.197  =  PbCOs 

PbO  X  1.08     =Pb(OH)2 

4.  Laboratory  Examination  of  Paste 

(a)  Caking  in  Container 

When  an  original  package  is  received  in  the  lab- 
oratory, it  shall  be  weighed,  opened,  and  stirred 
with  a  stiff  spatula  or  paddle.  The  paste  must  be 
no  more  difficult  to  break  up  and  show  no  more  cak- 
ing than  a  normal  good  grade  of  white  lead  paste. 
The  paste  shall  finally  be  thoroughly  mixed,  re- 
moved from  the  container,  and  the  container  wiped 
clean  and  weighed.  This  weight  subtracted  from 
the  weight  of  the  original  package  gives  the  net 
weight  of  the  contents.  A  portion  of  thoroughly 
mixed  paste  shall  be  placed  in  a  clean  container 
and  the  portions  for  the  remaining  tests  promptly 
weighed  out. 

(b)  Mixing  with  Linseed  Oil 

One  hundred  grams  of  the  paste  shall  be  placed 
in  a  cup,  30  c.c.  linseed  oil  added  slowly  with  care- 
ful stirring  and  mixing  with  a  spatula  or  paddle. 


Basic  Carbonate  of  Lead  103 

The  resulting  mixture  must  be  smooth  and  of  good 
brushing  consistency. 

(c)  Moisture  and  Other  Volatile  Matter 
Weigh  accurately  from  3  to  5  grams  of  the  paste 

into  a  tared  flat  bottomed  dish,  about  5  cm.  in  diam- 
eter, spreading  the  paste  over  the  bottom.  Heat 
at  105  to  110°  C.  for  one  hour,  cool  and  weigh.  Cal- 
culate loss  in  weight  as  percentage  of  moisture  and 
other  volatile  matter. 

(d)  Percentage  of  Pigment 

Weigh  accurately  about  15  grams  of  the  paste 
into  a  weighed  centrifuge  tube.  Add  20  to  30  c.c. 
"extraction  mixture"  (see  reagents),  mix  thor- 
oughly with  a  glass  rod,  wash  the  rod  with  more 
of  the  extraction  mixture,  add  enough  of  the  re- 
agent to  make  a  total  of  60  c.c.  in  the  tube.  Place 
the  tube  in  the  container  of  a  centrifuge,  surround 
with  water  and  counterbalance  the  container  of  the 
opposite  arm  with  a  similar  tube  or  a  tube  with 
water.  Whirl  at  a  moderate  speed  until  well  set- 
tled. Decant  the  clear  supernatant  liquid.  Repeat 
the  extraction  twice  with  40  c.c.  of  the  extraction 
mixture,  and  once  with  40  c.c.  of  ether.  After 
drawing  off  the  ether,  set  the  tube  in  a  beaker  of 
water  at  about  80°  C.,  or  on  top  of  a  warm  oven 
for  10  minutes,  then  in  an  oven  at  110  to  115°  C. 
for  two  hours.  Cool,  weigh,  and  calculate  the  per- 
centage of  pigment. 

( e)  Examination  of  Pigment 

Grind  the  pigment  from  (d)  to  a  fine  powder, 
pass  through  a  No.  80  sieve  to  remove  any ' '  skins, ' ' 


104       Chemical  Analysis  of  Lead  and  Its  Compounds 
preserve  in  a  stoppered  tube  and  apply  tests  3  (a), 


(f)  Preparation  of  Fatty  Acids 

To  about  25  grams  of  the  paste  in  a  porcelain 
casserole,  add  15  c.c.  of  aqueous  sodium  hydroxide 
(see  reagents)  and  75  c.c.  of  ethyl  alcohol,  mix  and 
heat  uncovered  on  a  steam  bath  until  saponifica- 
tion  is  complete  (about  one  hour).  Add  100  c.c. 
of  water,  boil,  add  an  excess  of  sulphuric  acid  of 
specific  gravity  1.2  (8  to  10  c.c.  will  usually  suffice), 
boil,  stir,  and  transfer  to  a  separatory  funnel  to 
which  some  water  has  been  previously  added. 
Draw  off  as  much  as  possible  of  the  acid  aqueous 
layer  and  lead  sulphate  precipitate,  wash  once  with 
water  ;  then  add  50  c.c.  of  water  and  50  c.c.  of  ether. 
Shake  very  gently  with  a  whirling  motion  to  dis- 
solve the  fatty  acids  in  the  ether,  but  not  so  vio- 
lently as  to  form  an  emulsion.  Draw  off  the 
aqueous  layer  and  wash  the  ether  layer  with  one 
15  c.c.  portion  of  water  and  then  with  5  c.c.  por- 
tions of  water  until  free  from  sulphuric  acid.  Then 
draw  off  the  water  layer  completely.  Transfer  the 
ether  solution  to  a  dry  flask,  add  25  to  50  grams 
of  anhydrous  sodium  sulphate.  Stopper  the  flask 
and  let  stand  with  occasional  shaking  at  a  tem- 
perature below  25°  C.  until  the  water  is  completely 
removed  from  the  ether  solution,  which  will  be 
shown  by  the  solution  becoming  perfectly  clear 
above  the  solid  sodium  sulphate.  Decant  this  clear 
solution  (if  necessary  through  a  dry  filter  paper) 
into  a  dry  100-c.c.  Erlenmeyer  flask.  Pass  a  rapid 


Basic  Carbonate  of  Lead  105 

current  of  dry  air  (pass  through  a  CaCl2  tower) 
into  the  mouth  of  the  Erlenmeyer  flask  and  heat 
at  a  temperature  below  75°  C.  on  a  dry  hot  plate 
until  the  ether  is  entirely  driven  off. 

Note. — It  is  important  to  follow  all  of  the  details,  since  ether  generally 
contains  alcohol  and  after  washing  with  water  always  contains  water.  It 
is  very  difficult  to  remove  water  and  alcohol  by  evaporation  from  fatty 
acids,  but  the  washing  of  the  ether  solution  and  subsequent  drying  with 
anhydrous  sodium  sulphate  removes  both  water  and  alcohol.  Ether,  in  the 
absence  of  water  and  alcohol,  is  easily  removed  from  fatty  acids  by  gentle 
heat. 

The  fatty  acids  prepared  as  above  should  be 
kept  in  a  stoppered  flask  and  examined  at  once. 

(g)  Test  for  Mineral  Oil 

Place  10  drops  of  the  fatty  acid  (/)  in  a  50  c.c. 
test  tube,  add  5  c.c.  of  alcoholic  soda  (see  reagents), 
boil  vigorously  for  five  minutes,  add  40  c.c.  of 
water  and  mix.  A  clear  solution  indicates  absence 
of  more  than  a  trace  of  unsaponifiable  matter.  If 
the  solution  is  not  clear,  the  oil  is  not  pure  linseed 
oil. 

(h)  Iodine  Number  of  Fatty  Acids 

Place  a  small  quantity  of  the  fatty  acids  4  (/) 
in  a  small  weighing  burette  or  beaker.  Weigh 
accurately.  Transfer  by  dropping  about  0.15  gram 
(0.10  to  0.20  gram)  to  a  500-c.c.  bottle  having  a 
well  ground  glass  stopper,  or  an  Erlenmeyer  flask 
having  a  specially  flanged  neck  for  the  iodine  test. 
Reweigh  the  burette  or  beaker  and  determine  the 
amount  of  sample  used.  Add  10  c.c.  of  chloroform. 
Whirl  the  bottle  to  dissolve  the  sample.  Add  10 
c.c.  of  chlorofrom  to  two  empty  bottles  like  that 
used  for  the  sample.  Add  to  each  bottle  25  c.c, 


106      Chemical  Analysis  of  Lead  and  Its  Compounds 

of  the  Harms  solution  (see  reagents)  and  let  it 
stand  with  occasional  shakings  for  one-half  hour. 
Add  10  c.c.  of  the  15  per  cent  potassium  iodide 
solution  and  100  c.c.  of  water,  and  titrate  with 
standard  sodium  thiosulphate,  using  starch  as  in- 
dicator. The  titration  on  the  two  blank  tests  should 
agree  within  0.1  c.c.  From  the  difference  between 
the  average  of  the  blank  titrations  and  the  titration 
on  the  sample,  and  the  iodine  value  of  the  thio- 
sulphate solution,  calculate  the  iodine  number  of 
the  sample  tested.  (Iodine  number  is  centigrams 
of  iodine  to  1  gram  of  sample.)  If  the  iodine  num- 
ber is  less  than  170,  the  oil  does  not  meet  the  speci- 
fication. 


' » 


(i)  Coarse  Particles  and  "Skins 

Weigh  an  amount  of  paste  containing  100  grams 
of  pigment  (see  4  (d)),  add  100  c.c.  kerosene,  wash 
through  a  No.  825  screen  and  weigh  the  residue  as 
in  3  (c).  The  total  residue  left  on  the  screen  should 
be  not  more  than  2.0  grams. 

5.  Reagents 

(a)  Extraction  Mixture 

10  volumes  ether  (ethyl  ether) 
6  volumes  benzol 
4  volumes  methyl  alcohol 
1  volume  acetone 

(b)  Aqueous  Sodium  Hydroxide 

Dissolve  100  grams  sodium  hydroxide  in  dis- 
tilled water  and  dilute  to  300  c.c. 


Basic  Carbonate  of  Lead  107 

(c)  Standard  Sodium  Thiosulphate  Solution 
Dissolve  pure  sodium  thiosulphate  in  distilled 

water  that  has  been  well  boiled  to  free  it  from  car- 
bon dioxide,  in  the  proportion  of  24.83  grams  crys- 
tallized sodium  thiosulphate  to  1000  c.c.  of  the 
solution.  It  is  best  to  let  this  solution  stand  for 
about  two  weeks  before  standardizing.  Standard- 
ize with  pure  resublimed  iodine.1  This  solution  will 
be  approximately  decinormal,  and  it  is  best  to 
leave  it  as  it  is  after  determining  its  exact  iodine 
value,  rather  than  to  attempt  to  adjust  it  to  exactly 
decinormal.  Preserve  in  a  stock  bottle  provided 
with  a  guard  tube  filled  with  soda  lime. 

(d)  Starch  Solution 

Stir  up  2  to  3  grams  of  potato  starch  or  5  grams 
of  soluble  starch  with  100  c.c.  of  1  per  cent  sali- 
cylic acid  solution,  add  300  to  400  c.c.  of  boiling 
water,  boil  the  mixture  until  the  starch  is  practi- 
cally dissolved,  and  then  dilute  to  one  liter. 

(e)  Potassium  Iodide  Solution 

Dissolve  150  grams  potassium  iodide  free  from 
iodate  in  distilled  water  and  dilute  to  1000  c.c. 

(f)  Hanus  Solution 

Dissolve  13.2  grams  of  iodine  in  1000  c.c.  of  gla- 
cial acetic  acid,  99.5  per  cent,  which  will  not  reduce 
chromic  acid.  Add  enough  bromine,  about  3  c.c., 
to  double  the  halogen  content,  which  is  determined 
by  titration.  The  iodine  may  be  dissolved  by  ap- 
plying heat,  but  the  solution  should  be  cold  when 
the  bromine  is  added. 


iSee  Treadwell-Hall  Analytical  Chemistry,  II,  3d  ed.,  p.  646. 


108      Chemical  Analysis  of  Lead  and  Its  Compounds 

(g)  Alcoholic  Sodium  Hydroxide  Solution 

Dissolve  pure  sodium  hydroxide  in  95  per  cent 
ethyl  alcohol  in  the  proportion  of  about  22  grams 
per  1000  c.c.  Let  the  solution  stand  in  a  stoppered 
bottle.  Decant  the  clear  liquid  into  another  bottle, 
and  keep  well  stoppered.  This  solution  should  be 
colorless  or  only  slightly  yellow  when  used,  and  it 
will  keep  colorless  longer  if  the  alcohol  is  pre- 
viously treated  with  NaOH  (about  80  grams  to 
1000  c.c.),  kept  at  about  50°  C.  for  15  days,  and 
then  distilled. 


CHAPTER    XI 

ELECTROLYTIC  DEPOSITION  OF  LEAD 

Lead  may  be  determined  electrolytically  in  a  very 
rapid  manner  by  following  the  procedure  as  out- 
lined by  Smith1  in  his  Electro-Analysis. 

The  Rapid  Precipitation  of  Lead  Dioxide  with 
the  Use  of  a  Rotating  Electrode 

"Twenty  c.c.  of  concentrated  nitric  acid  were 
added  to  a  solution  of  lead  nitrate,  giving  a  total 
volume  of  about  125  c.c.  and  acted  upon  with  a 
current  of  N.D.100  =  10  amperes  and  4.5  volts.  The 
rotating  electrode  (cathode)  performed  600  revo- 
lutions per  minute.  The  deposits  had  a  uniform, 
velvety  black  color.  There  was  no  tendency  on  the 
part  of  the  deposit  to  scale  off,  though  more  than  a 
gram  of  the  dioxide  was  precipitated.  The  time 
varied  from  ten  to  fifteen  minutes.  A  platinum 
dish  with  sand  blasted  inner  surface  was  used  as 
an  anode. 

By  using  a  current  of  N.  D.100  =  11  amperes  and 
4  volts  upon  a  solution  of  lead  nitrate  containing 
0.4996  gram  of  lead  or  0.5787  gram  of  dioxide,  the 
rate  of  precipitation  was  found  to  be : 

In  5  minutes .  .  0.4940  gram  lead  dioxide. 
In  10  minutes.  .0.5708  gram  lead  dioxide. 
In  15  minutes .  .  0.5747  gram  lead  dioxide. 

lElectro- Analysis,  Smith:    P.  Blakiston's  Sons  &  Co. 

109 


1 10      Chemical  Analysis  of  Lead  and  Its  Compounds 

In  20  minutes .  .  0.5770  gram  lead  dioxide. 
In  25  minutes.  .0.5787  gram  lead  dioxide. 
In  30  minutes.  .0.5789  gram  lead  dioxide. 

The  maximum  time  period  for  a  quarter  of  a 
gram  of  metal  is  fifteen  minutes,  and  the  maximum 
time  for  a  half  gram  of  metal  is  twenty-five  min- 
utes. " 


CHAPTER    XII 

STANDARD  METHODS  OF  CHEMICAL 
ANALYSIS  OF  PIG  LEAD1 

A.    Determination  of  Silver 

Weigh  100  grams  of  the  sample  into  a  3  inch 
scorifier  and  heat  in  a  muffle  furnace  until  the 
assay  ' '  covers. ' '  Pour  into  an  iron  mold  and  allow 
to  cool.  Free  the  resulting  lead  button  from  PbO, 
scorify  again  and  pour  as  before.  The  button  last 
obtained  should  not  weigh  over  20  grams  and  can 
be  cupelled  directly.  Weigh  the  silver  button  ob- 
tained upon  an  assay  balance. 

Note. — If  the  amount  of  silver  is  large,  the  button  should  be  examined  for 
gold,  in  the  usual  manner. 

B.    Determination  of  Bismuth 

Solutions  Required 

Sodium  Carbonate. — Dissolve  100  grams  Na2C0.3 
in  a  liter  of  distilled  water. 

Ammonium  Carbonate. —  Make  a  half  saturated 
solution. 

Alkaline  Sulphide  Wash  Solution. —  Dissolve 
200  grams  of  KOH  in  a  liter  of  distilled  water  and 
mix  one  part  of  this  solution  with  4  parts  of  H2S 
water. 


iReprinted  by  permission  from  the  1921  Book  of  the  A.  S.  T.  M. 
Standards  of  the  American  Society  for  Testing  Materials. 

Ill 


112       Chemical  Analysis  of  Lead  and  Its  Compounds 

Method 

(a)  Determination  for  Ordinary  Amounts  of 
Bismuth. 

Dissolve  20  grams  of  the  sample  in  a  400-c.c. 
beaker  with  100  c.c.  of  HNO3  (1:4),  with  the  aid 
of  heat.  When  solution  is  complete,  add  dilute 
ammonia  (1:2)  with  constant  stirring,  drop  by 
drop  from  a  burette,  until  a  faint  opalescence  ap- 
pears. If  an  actual  precipitate  is  formed,  redis- 
solve  by  the  addition  of  a  small  amount  of  HN03 
(1:4)  and  repeat  the  addition  of  ammonia.  Now 
add  5  c.c.  of  HC1  (1:9),  fill  the  beaker  with  hot 
water,  bring  to  boiling,  and  allow  to  stand  on  a 
steam  bath  for  two  hours.  The  assay,  while  stand- 
ing, must  not  reach  the  boiling  temperature.  Filter 
through  a  7-cin.  paper.  Transfer  the  precipitate 
completely  to  the  paper  by  means  of  a  "  police- 
man "  and  wash  twice  with  hot  water.  Carefully 
examine  the  filtrate,  washings,  and  any  decanted 
liquid  and  reject  if  clear.  Dissolve  the  precipitate 
by  dropping  around  the  edges,  from  a  5-c.c.  pipette, 
5  c.c.  of  boiling  HC1  (1:9),  receiving  the  solution 
in  the  original  beaker.  Wash  the  paper  thoroughly 
with  hot  water,  fill  the  beaker  with  water,  bring 
to  boiling,  and  allow  to  stand  as  before.  Filter  the 
bismuth  oxychloride  upon  a  weighed  Gooch  cru- 
cible, wash  thoroughly  with  water,  once  with  alco- 
hol, once  with  ether,  and  dry  upon  the  hot  plate. 
Cool  and  weigh. 

Note — If  time  permits,  it  is  convenient  to  allow  the  assay  to  stand  over 
night.  In  that  case,  the  precipitate  of  bismuth  oxychloride  generally  settles 
so  completely  that  the  clear  supernatant  solution  can  be  decanted. 


The  Analysis  of  Pig  Lead  1 13 

(b)  Determination  for  Amounts   of  Bismuth 
Smaller  Than  Can  Be  Determined  by  (a). 

Dissolve  100  grams  of  the  sample  in  500  c.c.  of 
dilute  HN03  (1:4).  When  solution  is  complete, 
allow  to  cool  and  add  Na2C03  solution  little  by  lit- 
tle until  a  slight  permanent  precipitate  has  formed. 
Then  add  50  c.c.  of  the  Na2C03  solution,  bring  to 
boiling,  allow  to  stand  warm  until  the  supernatant 
liquor  is  clear  again,  filter  and  reject  the  filtrate. 
Dissolve  the  precipitate  without  washing  by  slowly 
pouring  hot  HN03  (1:4)  around  the  edges  of  the 
filter  paper,  using  no  more  acid  than  necessary. 
Wash  the  paper  once  with  hot  water  and  determine 
bismuth  in  the  filtrate  as  described  in  (a). 

Note. — When  the  sample  contains  a  small  amount  of  bismuth,  it  is  often 
difficult  to  ascertain  when  the  correct  amount  of  ammonia  has  been  added 
to  the  nitrate  solution.  In  this  case,  place  a  small  piece  of  litmus  paper 
in  the  solution  and  add  the  ammonia  very  gradually  until  the  litmus  paper 
indicates  a  neutral  reaction. 

(c)  Determination  of  Bismuth  in  Samples  Con- 
taining Appreciable  Amounts  of  Tin  and  Anti- 
mony. 

Use  a  piece  of  litmus  paper  as  in  Note  under 
(b),  and  after  the  first  precipitation  of  bismuth 
oxy chloride  has  been  filtered  off  and  washed  (see 
(a))  proceed  as  follows :  Dissolve  the  bismuth  by 
dropping  around  the  edges  of  the  paper  10  c.c.  of 
boiling  HC1  (1:2),  receiving  the  solution  in  the 
original  beaker.  Discard  the  paper  after  washing. 
Dilute  the  solution  to  about  200  c.c.  with  fresh 
PLS  water  and  then  pass  ILS  gas  through  the  hot 
solution  for  fifteen  minutes.  Filter  and  wash  with 


1 14      Chemical  Analysis  of  Lead  and  Its  Compounds 

hot  water.  Remove  any  tin  or  antimony  present 
by  washing  three  times  with  alkaline  sulphide  wash 
solution.  Wash  the  precipitate  again  with  hot 
water,  place  it,  together  with  the  filter  paper,  in  a 
100-c.c.  beaker,  add  20  c.c.  of  HN03  (1 :4),  boil  until 
sulphides  are  completely  dissolved  and  the  paper 
well  pulped.  Filter  the  solution,  receiving  the  fil- 
trate in  the  original  beaker,  and  wash  well.  Deter- 
mine bismuth  in  the  filtrate  as  in  (a). 

Notes. — When  the  sample  contains  comparatively  large  amounts  of  tin 
or  antimony,  the  residue  left  after  the  solution  of  the  lead  in  the  nitric 
acid  obscures  the  opalescencc  found  upon  the  addition  of  ammonia. 

If  the  original  sample  contains  more  than  0.25  per  cent  of  bismuth,  it  is 
preferable  to  use  only  a  10  gram  charge. 

C.   Determination  of  Arsenic 

Method 

Dissolve  111.11  grams  of  the  sample  in  550  c.c. 
of  HNO.;  (1:4).  When  solution  is  complete  wash 
into  a  graduated  liter  flask.  Add  75  c.c.  of  H2S04 
(1:1),  cool,  and  make  up  to  the  mark  with  water. 
Transfer  to  a  large  beaker,  rinsing  out  the  flask 
with  25  c.c.  of  water.  Mix  thoroughly,  allow  to 
settle  and  filter  off  900  c.c.,  equivalent  to  a  100 
gram  charge.  Evaporate  in  a  large  porcelain  dish 
until  only  enough  H2SO4  is  left  to  moisten  the  resi- 
due. When  cool,  wash  into  a  small  distilling  flask 
with  60  c.c.  of  HC1  (specific  gravity  1.20)  and  20 
c.c.  of  water,  cleaning  the  dish  carefully.  Add  10 
grams  of  ferrous  sulphate  and  distill,  boiling  to 
as  small  volume  as  possible.  When  cool  add  50  c.c. 
more  HC1  (specific  gravity  1.20)  and  redistill. 
Pass  H2S  gas  through  the  cold  distillate  for  45 
minutes.  Filter,  and  weigh  the  As,S3  on  a  Gooch 


The  Analysis  of  Pig  Lead  1 15 

crucible,  washing  in  cold  water,  alcohol  and  CS«. 
After  drying  and  weighing,  redissolve  with 
(NH4)2C03  solution  and  reweigh  the  Gooch  cru- 
cible, calculating  the  loss  in  weight  to  arsenic. 

Note. — The  25  c.c.  of  water  added  is  equivalent  to  the  volume  of  precipi- 
tated lead  sulphate. 

D.   Determination  of  Remaining  Metals 

Solutions  Required 

Tartaric  Acid. —  Dissolve  50  grams  of  tartaric 
acid  in  250  c.c.  of  distilled  water  to  which  has  been 
added  250  c.c.  HC1  (specific  gravity  1.20). 

Method 

Dissolve  222.23  grams  of  the  sample  in  1100  c.c. 
of  HN03  (1:4),  using  a  1300-c.c.  beaker.  When 
solution  is  complete  examine  for  color  and  turbid- 
ity. If  clear,  wash  the  solution  at  once  into  a  2000- 
c.c.  graduated  flask.  In  case  of  a  residue  (Note 
1),  however,  dilute  to  about  1100  c.c.  and  allow  to 
stand  until  the  supernatant  liquor  is  clear.  De- 
cant as  much  as  possible  into  a  2000-c.c.  flask, 
filter  the  remainder  and  receive  the  filtrate  in  the 
same  flask.  Wash  the  precipitate  well  and  then 
place  it;  together  with  the  filter  paper,  in  a  100-c.c. 
beaker  and  add  20  c.c.  of  the  tartaric  acid  mix- 
ture. Heat  to  boiling  and  when  the  paper  is  well 
pulped  allow  to  digest  warm  for  30  minutes.  Now 
add  50  c.c.  of  hot  water,  filter  and  wash.  (Note 
2.)  Carefully  dry  the  residue  and  ignite.  If  any 
appreciable  residue  remains,  brush  it  into  a  small 
silver  dish  containing  1  gram  of  molten  KOH. 
Fuse  for  5  minutes,  and  after  cooling  dissolve  in 


116       Chemical  A  nalysis  of  Lead  and  Its  Compounds 

as  little  hot  water  as  possible  and  add  to  the  above 
mentioned  tartaric  acid  filtrate.  Render  this  solu- 
tion just  alkaline  with  ammonia  and  then  just  acid 
with  HC1,  and  saturate  hot  with  HL,S  gas.  After 
digesting  for  30  minutes  on  the  steam  bath,  pass 
ILS  through  the  solution  again  for  15  minutes. 
Filter  and  wash  with  slightly  acidified  ILS  water. 
Reject  the  filtrate.  Wash  the  sulphides  from  the 
paper  into  the  original  beaker  and  add  5  c.c. 
of  KOH  solution  (1:5)  for  every  25  c.c.  volume 
present.  Digest  hot  for  5  minutes  and  filter 
through  the  original  paper  into  a  small  flask  grad- 
uated to  110  c.c.  After  washing  with  ELS  water 
containing  a  little  of  the  KOH  solution,  cool  the 
filtrate  and  make  up  to  the  mark.  Mix  and  reserve 
100  c.c.  as  alkaline  sulphide  solution  No.  1.  The 
precipitate  may  be  discarded. 

Add  slowly  to  the  main  solution  in  the  2000-c.c. 
flask  150  c.c.  of  H2S04  (1:1).  After  cooling  and 
filling  up  to  the  mark,  pour  into  a  clean  3-liter 
flask  provided  with  a  rubber  stopper.  Rinse  the 
flask  out  with  50  c.c.  of  water,  which  is  equivalent 
to  the  volume  of  lead  sulphate  present  and  is  added 
to  the  portion.  After  mixing  thoroughly  by  shak- 
ing, allow  the  precipitate  to  settle  and  filter  off 
1800  c.c.  of  the  liquid.  This  is  equivalent  to  a 
200  gram  charge.  Place  this  in  a  No.  9  porcelain 
evaporating  dish  and  evaporate,  first  over  a  free 
flame  and  later  on  the  hot  plate  until  only  enough 
HoS04  is  left  to  moisten  the  residue  remaining. 
Add  50  c.c.  of  water  and,  after  digesting  warm  for 
a  short  time,  wash  the  solution  into  a  250-c.c. 


The  Analysis  of  Pig  Lead  117 

beaker,  cleaning  the  dish  carefully.  Allow  the 
solution  to  digest  on  the  steam  bath  for  4  or  5 
hours.  (Note  3.)  Then  filter,  wash  and  evaporate 
the  filtrate  to  200-250  c.c.  Place  any  residue  (Note 
4),  together  with  the  filter  paper,  in  a  100-c.c. 
beaker  and  treat  with  20  c.c.  of  the  tartaric  acid 
mixture.  Boil  for  5  minutes,  dilute  with  50  c.c. 
of  hot  water  and  filter.  Make  the  filtrate  alkaline 
with  ammonia  and  just  acid  with  HC1,  and  obtain 
the  tin,  antimony  and  arsenic  as  previously  de- 
scribed, reserving  the  whole  of  the  alkaline  sul- 
phide solution  as  solution  No.  2.  Reject  the  sul- 
phide residue. 

To  filtrate  from  the  lead  sulphate,  add  ammonia 
until  the  neutral  point  is  reached,  and  then  for 
every  50  c.c.  of  the  solution  present  add  2  c.c.  of 
HC1  (specific  gravity  1.20).  Pass  H2S  gas  into 
the  hot  solution  until  saturated,  digest  for  30  min- 
utes on  the  steam  bath  and  again  pass  H2S  gas 
into  the  solution.  Filter  and  wash  with  H2S  water 
slightly  acidified.  (Note  5.)  Separate  tin,  anti- 
mony and  arsenic  in  the  precipitate  with  KOH 
solution  as  usual,  obtaining  an  alkaline  sulphide 
solution  No.  3.  (Note  6.) 

To  sum  up,  three  alkaline  sulphide  solutions 
have  been  obtained,  containing  tin,  antimony  and 
arsenic,  a  precipitate  of  metallic  sulphides  contain- 
ing copper,  lead,  etc.,  and  a  solution  containing 
iron,  zinc,  nickel,  etc. 

Notes. — 1.  A  residue  indicates  the  presence  of  antimony,  tin  possibly 
arsenic,  or  sulphur  as  lead  sulphate. 

2.  It  has  been  found  that  even  this  treatment  occasionally  fails  to  dis- 
solve stannic  acid  completely. 


1 18       Chemical  Analysis  of  Lead  and  Its  Compounds 

3.  If   it  is   preferred,   allow   solution   to   stand   over   night   to  insure   the 
complete  solution  of  all  soluble  salts. 

4.  Any    residue   of    lead   sulphate    may   contain    some    tin,    antimony,    or 
possibly  arsenic. 

5.  The  filtrate  will  contain  any  iron,  zinc,  nickel,  cobalt  and  manganese  ; 
while   in   the   precipitate  will   be   found   any   copper,   cadmium,   lead,   silver, 
bismuth,  tin,  antimony  and  arsenic. 

6.  When    separating    the   sulphides    of   arsenic,    antimony    and    tin    from 
sulphides   of   copper,    lead,   etc.,    it   is    necessary    to    wash    all   the   sulphides 
back    into   the   beaker    in    which    they    were    precipitated.      These    sulphides 
sometimes  cling  so  tenaciously  to  the  paper  that  in   dislodging  them  more 
water  than  the  25  c.c.  specified  is  required.     In  this  case  allow  the  sulphides 
to   settle   and   then   decant   the   clear   supernatant   liquor   through   the    filter 
until  the  volume  is  reduced  to  25  c.c.     Before  rejecting  decanted  fluid  always 
test  with  H2S  water. 

In  washing  sulphide  precipitates  with  water,  much  trouble  is  experienced 
from  the  tendency  of  the  precipitate  to  pass  through  the  filter  in  the  col- 
loidal form.  This  is  particularly  true  in  washing  sulphides  that  have  been 
digested  with  KOH.  Time  and  trouble  will  be  saved  by  washing  all  the 
sulphides  precipitated  from  mineral  acid  solutions  with  H-S  water  contain- 
ing a  little  of  the  acid  in  which  they  were  precipitated.  The  same  is  true 
of  sulphides  precipitated  in  or  filtered  from  alkaline  solution. 

When  working  with  alkaline  solutions  in  which  tin  is  to  be  determined, 
avoid  the  use  of  Jena  or  other  glass  that  contains  zinc.  The  zinc  content 
of  the  glass  may  influence  the  result. 

Determination  of  Antimony  and  Tin 

Solutions  Required 

Potassium  Iodide. —  Dissolve  100  grams  in  a 
liter  of  distilled  water. 

Standard  Sodium  Thiosulphate. —  Dissolve  24.8 
grams  of  Na2S203.5H20  in  1000  c.c.  of  distilled 
water,  and  allow  to  stand  for  24  hours.  Stand- 
ardize against  Antimony  Metal,  c.  p.,  using  same 
quantity  of  reagents  and  same  procedure  as  under 
method.  Each  cubic  centimeter  is  equivalent  to 
approximately  0.006  gram  of  antimony. 

Method 

Wash  the  alkaline  sulphide  solutions  Nos.  1,  2, 
and  3  into  a  600-c.c.  beaker,  and  acidify  with  5  c.c. 
of  HN03  (specific  gravity  1.42)  and  20  c.c.  of  HC1 


The  Analysis  of  Pig  Lead  119 

(specific  gravity  1.20).  Evaporate  the  solution  to 
dryness  on  the  steam  bath.  Dissolve  the  residue 
in  200  c.c.  of  water,  add  10  grams  of  oxalic  acid 
and  10  grams  ammonium  oxalate  and  heat  the  solu- 
tion until  it  is  clear.  Then  pass  H2S  gas  through 
the  boiling  solution  for  45  minutes.  Filter  off  the 
precipitate,  consisting  of  arsenic  and  antimony  sul- 
phides, and  wash  with  hot  water.  Determine  tin 
electrolytically  in  the  filtrate,  continuing  the  elec- 
trolysis until  all  the  oxalic  acid  is  decomposed  and 
the  solution  becomes  alkaline.  Dissolve  the  deposit 
on  the  cathode  with  a  small  amount  of  HC1  and 
examine  qualitatively  for  tin. 

Dissolve  the  sulphides  of  arsenic  and  antimony 
in  KOH  as  usual,  collecting  the  filtrate  in  a  500-c.c. 
Erlenmeyer  flask.  Add  50  c.c.  of  HC1  (specific 
gravity  1.20)  and  boil  the  solution  until  about  30 
c.c.  are  left.  Expel  the  arsenic  as  chloride.  Now 
oxidize  the  solution  with  a  pinch  of  KC103  and  boil 
until  no  more  chlorine  remains.  Cool  and  add  5 
c.c.  potassium  iodide  solution.  Titrate  the  liberated 
iodine  with  N/10  sodium  thiosulphate  solution, 
using  carbon  disulphide  as  an  indicator. 

Determination  of  Copper  and  Cadmium 

Solutions  Required 

Sodium  Chloride  (Solution  No.  1). —  Dissolve  1 
gram  NaCl  in  100  grams  distilled  water. 

Sodium  Chloride  (Solution  No.  2). —  Dissolve  10 
grams  Nad  in  100  grams  distilled  water. 

Standard  Potassium  Cyanide. —  Dissolve  2 
grams  of  KCN  in  a  liter  of  distilled  water  and 


120       Chemical  Analysis  of  Lead  and  Its  Compounds 

standardize  against  a  known  amount  of  copper  as 
treated  in  the  analysis. 

Sodium  Carbonate  (Solution  No.  1). —  Dissolve 
50  grams  Na2C03  in  1  liter  of  distilled  water. 

Sodium  Carbonate  (Solution  No.  2). —  Dissolve 
Na2CO.?  in  distilled  water  to  saturation. 

Method 

(a)  Determination  Where  Copper  Exceeds 
0.0025  per  cent. 

Place  the  filter  containing  the  sulphides  in  a  100- 
c.c.  beaker  and  add  20  c.c.  of  HNO3  (1:4).  Heat 
with  occasional  stirring  until  the  paper  is  thor- 
oughly pulped  and  the  sulphides  are  completely 
dissolved.  Filter  into  a  250-c.c.  beaker.  Dry  the 
residue,  which  generally  contains  a  small  amount 
of  copper,  ignite  in  a  porcelain  crucible,  boil  with 
5  c.c.  of  HN03  (1:1),  and  wash  into  the  main  por- 
tion, keeping  the  volume  below  100  c.c.  Render 
it  strongly  alkaline  with  ammonia,  and  add  5  grams 
of  potassium  cyanide,  then  saturate  it  in  the  cold 
with  H2S  gas.  (Note  1.)  Filter  the  solution  and 
evaporate  the  filtrate  to  a  volume  of  20  to  30  c.c. 
in  a  4  inch  porcelain  casserole.  Boil  until  solu- 
tion is  complete.  Add  20  c.c.  of  H2SO4  (1:1)  and 
evaporate  the  solution  under  a  hood  until  dense 
fumes  of  H2S04  escape.  Cool,  dilute,  and  warm 
until  copper  sulphate  is  all  dissolved.  Now  filter, 
if  necessary,  into  a  200-c.c.  beaker,  render  just 
alkaline  with  ammonia,  make  acid  by  the  addition 
of  3  c.c.  of  HNOo  per  100  c.c.  solution,  and  electro- 
lyze  for  copper. 


The  Analysis  of  Pig  Lead  121 

Dissolve  the  precipitate  of  sulphides  in  the  usual 
manner  with  20  c.c.  of  HN03  (1:4).  Add  1  c.c. 
NaCl  solution  No.  1  to  the  solution,  still  contain- 
ing the  pulped  filter,  and  digest  for  one-half  hour. 
Filter  off  the  AgCl,  wash  and  reject.  Make  the 
filtrate,  not  exceeding  100  c.c.,  alkaline  with  a  slight 
excess  of  Na2CO.?  and  add  5  grams  of  KCN.  Di- 
gest for  1  hour.  Filter  and  wash  with  Na2C03 
solution  No.  1.  Reject  the  precipitate  of  bismuth. 
Now  add  a  few  cubic  centimeters  of  ammonium 
sulphide  solution  to  the  filtrate  to  precipitate  any 
cadmium  as  yellow  cadmium  sulphide.  Filter  upon 
a  weighed  Grooch  crucible  and  weigh  as  cadmium 
sulphide.  (Note  2.) 

Notes. — 1.  Copper  remains  in  the  solution  while  lead,  silver  and  bismuth 
and  cadmium  are  precipitated. 

2.  If  an  appreciable  amount  of  cadmium  sulphide  is  found,  it  should  be 
converted  to  and  weighed  as  cadmium  sulphate,  according  to  method  for 
cadmium  under  Standard  Methods  of  Chemical  Analysis  of  Spelter  (see 
page  130)  of  the  American  Society  for  Testing  Materials. 

(b)  Determination  Where  Copper  Is  Less  Than 
0.0025  Per  Cent. 

Place  the  paper  containing  the  sulphides  in  a 
porcelain  crucible,  dry  carefully  and  ignite.  When 
the  carbon  has  been  all  burned  off,  cool  and  dis- 
solve the  residue  in  5  to  10  c.c.  of  HN03  (1:1). 
After  evaporating  to  a  volume  of  1  to  2  c.c.,  add  1 
c.c.  of  H2S04  (1:1).  Then  evaporate  the  solution 
until  fumes  appear,  cool,  dilute,  add  a  few  drops 
of  NaCl  solution  No.  2,  and  filter  off  the  lead  sul- 
phate and  silver  chloride.  Again  evaporate  the 
filtrate  until  fumes  of  H2S04  appear,  and  when 
cold,  dilute  and  neutralize  with  Na2C03  solution  No. 


122      Chemical  Analysis  of  Lead  and  Its  Compounds 

2.  Then  add  about  six  drops  of  concentrated  am- 
monia and  titrate  the  solution  with  standard  KCN 
solution  until  the  blue  color  is  discharged. 

The  cadmium  can  be  obtained  by  making  this 
solution,  titrated  for  copper,  strongly  alkaline, 
diluting  a  little,  and  adding  5  grams  of  KCN.  Sat- 
urate the  solution  cold  with  H2S  gas,  filter,  discard 
the  filtrate  and  treat  the  precipitate  for  cadmium 
as  described  in  Method  (a). 

Determination  of  Iron 

Method 

Evaporate  the  filtrate  containing  iron,  zinc,  etc., 
to  100  c.c.  and  oxidize  with  a  few  drops  of  HNO;s. 
Separate  the  iron  with  ammonia  as  usual,  making 
two  separations,  and  receive  the  filtrate  in  a  500- 
c.c.  Erlenmeyer  flask.  Redissolve  the  iron  hydrox- 
ide with  hot  HC1  (1 :1)  or  dilute  H2S04  and  deter- 
mine the  iron  volumetrically  by  any  of  the  stand- 
ard methods. 

Determination  of  Zinc 

Method 

Add  to  the  filtrate  from  the  iron  hydroxide  1  c.c. 
of  cochineal  indicator,  and  render  just  neutral  with 
HC1.  Then  add  15  drops  of  twice  normal  HC1 
for  each  100  c.c.  of  the  solution.  Saturate  cold 
with  H2S  gas  and  allow  the  flask,  loosely  stoppered, 
to  stand  over  night.  Filter  and  wash  with  H2S 
water  acidified  in  the  same  manner  as  above  de- 
scribed. Dry  the  precipitate  of  zinc  sulphide,  care- 
fully ignite  in  a  porcelain  crucible  and  weigh  as 
zinc  oxide. 


The  Analysis  of  Pig  Lead  123 

Determination  of  Nickel  and  Cobalt 

Solutions  Required 

Hydrogen  Sulphide  Wash  Water. —  To  each  100 
c.c.  of  hydrogen  sulphide  water  add  20  c.c.  neutral 
ammonium  acetate. 

Method 

Eender  the  filtrate  just  alkaline  with  ammonia 
and  saturate  with  H2S.  Heat  to  boiling  and  then 
make  just  acid  with  acetic  acid,  add  20  c.c.  of  neu- 
tral ammonium  acetate  solution,  and  boil  until  the 
sulphides  of  nickel  and  cobalt  separate  out.  Filter 
and  wash  with  warm  H2S  wash  water.  Dry  the 
precipitate  and  paper  in  a  porcelain  crucible  and 
carefully  ignite.  If  there  is  an  appreciable  amount 
of  residue  after  ignition,  dissolve  by  boiling  with 
10  c.c.  of  aqua  regia,  wash  into  a  250-c.c.  beaker, 
add  10  c.c.  of  H2S04  (1:1),  evaporate  until  fumes 
appear,  cool,  dilute  to  200  c.c.,  make  alkaline  with 
ammonia,  and  add  15  c.c.  of  concentrated  ammonia. 
Then  electrolyze  the  solution  and  weigh  the  nickel 
and  cobalt  as  such. 

Notes — If  the  amount  of  nickel  and  cobalt  is  small  it  can  be  weighed  as 
oxide. 

If  the  filtrate  from  the  nickel  and  cobalt  sulphides  shows  a  brown  color, 
it  indicates  that  the  precipitation  has  not  been  complete.  In  this  case  render 
the  solution  ammoniacal  and  repeat  the  above  process. 

Determination  of  Manganese 

Solutions  Required 

Standard  Potassium  Permanganate. —  Mix  10 
c.c.  N/10  KMn04  and  100  c.c.  of  distilled  water. 
Each  cubic  centimeter  is  equivalent  to  approxi- 
mately 0.00011  gram  Mn. 


124      Chemical  Analysis  of  Lead  and  Its  Compounds 

Dilute  Sulphuric  Acid. —  Add  25  c.c.  concen- 
^rated  H2S04  to  1000  c.c.  of  distilled  water. 

Nitric  Acid  Wash.— Add  300  c.c.  HN03  to  1000 
c.c.  of  distilled  water. 

Method 

Evaporate  the  filtrate,  which  should  now  contain 
only  manganese,  to  dryness  in  a  porcelain  dish  and 
heat  carefully  over  an  Argand  burner  until  all  the 
ammonium  salts  have  been  driven  off.  (Note  1.) 
After  cooling,  moisten  the  residue  with  a  little  HC1 
and  warm  until  dissolved.  Add  1  c.c.  of  ILS04 
(1:1)  and  evaporate  the  solution  until  fumes  ap- 
pear, continuing  the  fuming  until  nearly  all  the 
H2S04  has  been  driven  off.  Cool,  and  add  50  c.c. 
of  HNO,  (1 :3)  and  0.5  gram  of  sodium  bismuthate. 
(Note  2.)  Boil  the  solution  until  the  pink  color  is 
destroyed.  If  any  manganese  is  precipitated,  dis- 
solve by  the  addition  of  a  few  cubic  centimeters 
of  a  dilute  sodium  thiosulphate  solution.  In  this 
case  the  solution  must  be  again  boiled  until  freed 
from  all  fumes.  After  cooling,  add  an  excess  of 
sodium  bismuthate,  stir  a  few  minutes  and  filter 
through  ignited  asbestos  into  a  100-c.c.  Nessler 
tube.  Wash  with  dilute  HNO.{  (Nitric  Acid  wash) 
and  make  the  filtrate  up  to  the  mark.  Into  another 
similar  tube  put  100  c.c.  of  dilute  H,S04  which 
has  been  made  very  faintly  pink  with  potassium 
permanganate  solution.  Now  add  standard  solu- 
tion of  potassium  permanganate  from  a  burette 
until  the  color  of  the  sample  is  exactly  matched. 

Notes — 1.  It  is  best  to  bake  here  over  a  Bunsen  flame  until  all  the 
organic  matter  has  been  destroyed. 

2.  The  HNO;i  must  be  freed  from  nitrous  fumes  by  passing  a  current 
of  air  through  the  acid  for  one-half  hour. 


CHAPTER    XIII 

STANDARD  METHODS  OF  CHEMICAL 
ANALYSIS  OF  SPELTER1 

The  methods  that  follow  are  based  on  the  Report 
of  the  Sub-Committee  on  Methods  of  Analysis  of 
Non-Ferrous  Alloys  for  the  Division  of  Industrial 
Chemists  and  Chemical  Engineers  of  the  American 
Chemical  Society,  approved  by  the  Supervisory 
Committee  on  Standard  Methods  of  Analysis  of 
that  Society.2  These  methods  were  originally  pro- 
posed by  Elliott  and  Storer3  and  Price,4  whose 
work  has  been  checked  and  elaborated  by  the  mem- 
bers of  the  Committee  of  the  American  Chemical 
Society  and  of  this  Society. 

The  methods  are  those  generally  accepted  in  the 
United  States  for  standard  analysis  in  all  the  large 
laboratories  of  both  producers  and  consumers  of 
zinc  and  zinc  products. 

The  Electrolytic  and  Lead  Acid  methods  de- 
scribed below  are  believed  to  be  of  equal  merit,  so 
far  as  accuracy  is  concerned,  but  where  labora- 
tories are  equipped  for  electrolysis  the  electro- 
lytic method  is  preferred  as  a  time  saver. 

lEeprinted  by  permission  from  the  1921  Book  of  A.  S.  T.  M. 
Standards  of  the  American  Society  for  Testing  Materials.  Adopted, 
1911;  Eevised  and  Printed  as  Separate  Standard,  1921. 

2 Journal  of  Industrial  and  Engineering  Chemistry,  Vol.  7,  1915, 
p.  547. 

3Memoirs,  Am.  Acad.  Arts  and  Sciences,  8,  Part  1,  May  20 
(1860). 

4The  Chemical  Engineer,  9  (1909),  4. 

125 


126       Chemical  Analysis  of  Lead  and  Its  Compounds 

Determination  of  Lead  by  the  Electrolytic 
Method 

Apparatus 

Platinum  cylindrical  gauze  electrodes  contain- 
ing approximately  400  meshes  per  sq.  cm.  (50 
meshes  per  linear  inch)  are  recommended  for 
anode  and  cathode.  They  should  be  stiffened  by 
doubling  the  gauze  for  about  3  mm.  at  the  top  and 
bottom  of  the  cylinders.  The  anode  should  be  ap- 
proximately 30  mm.  in  diameter  and  30  mm.  in 
height.  The  stem  should  be  made  from  1.14  mm. 
or  1.29  mm.  wire,  flattened  and  electrically  welded 
the  entire  width  of  the  gauze;  the  height  over  all 
should  be  approximately  130  mm.,  and  the  gauze 
should  be  sand  blasted.  The  cathode  should  be 
approximately  12  mm.  in  diameter  by  30  mm.  in 
height,  the  stem  being  of  the  same  dimensions  and 
welded  in  the  same  way  as  the  anode. 

Method 

Place  8.643  grams  (Note  1)  of  the  sample  in  a 
400-c.c.  beaker,  add  sufficient  water  to  cover  and 
then  add  30  c.c.  HNO;{  (specific  gravity  1.42)  grad- 
ually. When  action  is  complete,  boil  the  solution 
for  10  minutes,  wash  off  the  watch  glass  and  trans- 
fer the  solution  to  a  200-c.c.  electrolytic  beaker, 
washing  out  the  original  400-c.c.  beaker.  Dilute 
to  125  c.c.  and  electrolyze  (Note  2)  with  a  current 
of  five  amperes  for  45  minutes.  (Note  3.)  Test 
the  solution  for  complete  precipitation  of  lead  by 
washing  the  watch  glasses  and  sides  of  the  beaker, 
increasing  the  depth  of  the  solution  about  12  mm. 
Continue  the  current  for  15  minutes  and  if  the 
newly  exposed  surface  is  still  bright,  wash  the 


The  Analysis  of  Spelter  127 

anode  (Note  4)  three  or  four  times  with  distilled 
water,  once  with  alcohol,  and  then  dry  in  an  oven 
(Note  5)  at  210°  C.  for  30  minutes,  cool  in  a  dessi- 
cator  and  weigh. 

The  weight  of  the  deposited  PbO,  in  milligrams, 
divided  by  100,  gives  the  percentage  of  lead 
(Note  6). 

Notes. — 1.  The  empirical  factor  weight,  8.643  grams,  is  used  instead  of 
the  theoretical  one  (8.660  grams),  as  dried  dioxide  contains  some  adherent 
and  included  water,  not  entirely  expelled. 

2.  Before  electrolyzing,   the   beaker  should   be   covered   with  split   watch 
glasses  to  prevent  loss  by  spraying. 

3.  The  time  required  for  complete  deposition  is  usually  30  to  45  minutes. 
For  small  amounts  of  lead  30  minutes  will  be  found  sufficient. 

4.  The  washing  should  be  done  immediately,  as  the  deposit  of  PbO^  tends 
to  dissolve. 

5.  The  anode  may  also  be  dried  on  a  hot  plate,  although  a  drying  oven 
is  to  be  preferred. 

6.  The  PbO2  deposit  can  be  readily  removed  by  immersing  the  anode  in 
hot  dilute  solution  of  HNO3  to  which  oxalic  acid  has  been  added,  or  by  cover- 
ing with  dilute  HNO3  and  inserting  a  rod  of  copper. 


Determination  of  Lead  by  the  Lead  Acid 
Method 

Solutions  Required 

Lead  Acid.— POUT  300  c.c.  of  H2S04  (specific 
gravity  1.84)  into  1800  c.c.  of  distilled  water;  dis- 
solve 1  gram  of  lead  acetate  in  300  c.c.  of  distilled 
water  and  add  to  the  acid  solution  with  stirring. 
Allow  to  settle  for  several  days  and  siphon  off 
the  clear  solution  through  a  thick  asbestos  pad. 
(Note  1.) 

Nitric  Acid.-M.ix  1000  c.c.  of  HN03  (specific 
gravity  1.42)  with  1000  c.c.  of  distilled  water. 

Alcohol. —  Mix  1000  c.c.  of  ethyl  alcohol  (95  per 
cent)  with  1000  c.c.  of  distilled  water. 


128       Chemical  Analysis  of  Lead  and  Its  Compounds 

Method 

Place  sample  (Note  2)  of  25,  15,  10,  or  5  grams 
in  a  350-c.c.  beaker  and  add  300, 180, 120,  or  60  c.c., 
respectively,  of  lead  acid.  After  all  but  about  1 
gram  is  dissolved,  filter  on  a  close  filter  and  wash 
out  the  beaker  twice  with  lead  acid  from  a  wash 
bottle.  Wash  the  undissolved  matter  from  the  fil- 
ter into  the  original  beaker  with  water  and  dis- 
solve with  10  c.c.  of  HNO:{.  Add  40  c.c.  of  lead 
acid,  and  evaporate  until  copious  fumes  of  H2SO4 
are  evolved.  When  cool,  add  35  c.c.  (Note  3)  of 
water,  heat  to  boiling  and  add  the  first  filtrate 
(Note  4),  stir  well  and  allow  to  stand  over  night 
(Note  5).  Filter  on  a  Gooch  crucible,  wash  with 
lead  acid,  then  with  alcohol  water  mixture,  and 
finally  with  alcohol  alone.  Set  the  Gooch  crucible 
inside  of  a  larger  porcelain  crucible  (Note  6)  and 
heat  for  five  minutes  at  the  full  heat  of  a  Tirrill 
burner.  Cool  and  weigh  as  PbS04. 

Notes. — 1.  When  lead  acid  is  used,  it  is  unnecessary  to  consider  the 
solubility  of  PbSO4,  since  the  solution  is  always  brought  back  to  the  same 
volume  as  the  lead  acid  used  originally,  consequently  it  will  retain  no 
PbSO4  from  the  sample. 

2.  The  amount  of  sample  taken  is  governed  by  the  grade  of  spelter : 

Grade  No.   1,   25   grams.      Grade  No.   3,   10   grams. 

Grade  No.   2,   15   grams.     Grade   No.   4,     5   grams. 

Grade  No.  5,  5  grams. 

3.  The  35  c.c.  of  water  added  is  the  quantity  of  water  evaporated  from 
the  lead  acid. 

4.  The   first  filtrate,   which   contains   the   greater  part   of  the   zinc,   may 
also  contain  a  small  amount  of  PbSO4. 

5.  It    is   preferable   to   allow    the   solution   and    precipitate    of    PbSO^    to 
stand   over   night,   although   this   time   may   be   shortened    to    not    less   than 
five  hours. 

6.  The  Gooch  crucible  is  heated  inside  of  a  porcelain  crucible  to  avoid  re- 
duction of  the  PbSOi  by  flame  gases  and  mechanical  disintegration  of  the 
asbestos  mat. 


The  Analysis  of  Spelter  129 

Determination  of  Iron 

Solution  Required 

Dilute  Ammonia  Water.— Mix  100  c.c.of  NH4OH 
(specific  gravity  0.90)  with  1000  c.c.  of  distilled 
water. 

Sulphuric  Acid  (1:4).—  Mix  250  c.c.  of  H2S04 
(specific  gravity  1.84)  with  1000  c.c.  of  distilled 
water. 

Sulphuric  Acid  (1:1).—  Mix  500  c.c.  of  H2S04 
(specific  gravity  1.84)  with  500  c.c.  of  distilled 
water. 

Dilute  Sulphuric  Acid  for  Reductor. —  Mix  50 
c.c.  of  H,S04  (specific  gravity  1.84)  with  1000  c.c. 
of  distilled  water.  This  solution  is  used  boiling 
hot. 

Potassium  Permanganate. —  Dissolve  0.2  grain 
of  KMnO4,  c.  p.,  in  1000  c.c.  of  distilled  water. 
Allow  to  stand  for  several  days  in  a  glass  stop- 
pered bottle  in  a  dark  closet  and  then  filter  through 
prepared  asbestos.  Standardize  against  0.020 
gram  portions  of  pure  sodium  oxalate,  dissolved 
in  200  c.c.  of  the  dilute  H2SO4  for  reductor.  Each 
cubic  centimeter  of  KMn04  is  equivalent  to  ap- 
proximately 0.00033  gram  of  iron. 

Method 

Place  25  grams  of  the  sample  in  a  tall  700-c.c. 
beaker  and  dissolve  cautiously  with  125  c.c.  of 
HN03  (specific  gravity  1.42).  Boil,  dilute  to  about 
300  c.c.,  add  10  grams  of  NH4C1  and  then  ammonia 
water  (specific  gravity  0.90)  until  the  precipitated 
Zn(OH):>  has  redissolved.  Boil,  let  settle  and  fil- 


130      Chemical  Analysis  of  Lead  and  Its  Compounds 

ter  on  an  11-cm.  filter  paper  (Note  1).  Wash  with 
dilute  ammonia  water  and  then  with  hot  water 
until  free  from  chlorides.  Dissolve  precipitate 
from  the  paper  with  hot  H2S04  (1:4),  add  40  c.c. 
of  HoS04  (1 :1),  cool,  and  pass  through  a  Jones  re- 
ductor  (Note  2).  Wash  out  the  reductor  first  with 
150  c.c.  of  dilute  H2SO4  for  reductor  and  then  with 
100  c.c.  of  distilled  water  and  titrate  with  a  stand- 
ard KMn04  solution  (Note  3). 

Notes.— 1.  A  filter  paper  which  will  retain  Fe(OH)3  and  filter  rapidly 
should  be  used.  Whenever  the  amount  of  iron  is  at  all  large  or  when  great 
accuracy  is  demanded,  a  second  precipitation  of  Fe(OH)3  should  be  made 
by  dissolving  the  precipitate  on  the  paper  in  hot  dilute  HC1,  adding  am- 
monia water  and  filtering,  in  order  to  remove  all  traces  of  nitrates. 

2.  The  reductor  should  be  clean,  preferably  washed  out  with   150  c.c.  of 
dilute  HoSO*  and  100  c.c.  of  water  first.     If,  before  passing  through  the  re- 
ductor, a  large  amount  of  PbSO*  is  present,  it  is  well  to  filter  it  off  so  as 
to  prevent  it  from  clogging  the  reductor.     A  small  quantity  of  liquid  should 
always  be  left  in  the  reductor  funnel,   and  air  should  never  be  allowed  to 
enter  the  body  of  the  reductor.     For  description  and  further  details  of  use  of 
reductor,  see  "The  Chemical  Analysis  of  Iron,"  by  A.  A.   Blair,  or   "Quan- 
titative Chemical  Analysis,"  by  H.  P.  Talbot. 

3.  A  blank  determination  should  be  made  on  corresponding  amounts   of 
acid  and  water  passed  through  the  reductor  and  the  results  should  be  cor- 
rected accordingly.     About  0.5  c.c.  of  the  KMnO4  solution   will  be  required 
to  give  a  permanent  coloration  to  the  solution. 

Determination  of  Cadmium  Gravimetrically 

Solutions  Required 

Sulphuric  Acid  (l:l).—  M.ix  500  c.c.  of  H,S04 
(specific  gravity  1.84)  with  500  c.c.  of  distilled 
water. 

Sulphuric  Acid  (l:5).—  M.ix  200  c.c.  of  H,SOt 
(specific  gravity  1.84)  with  1000  c.c.  of  distilled 
water. 

Hydrochloric  Acid  (1:3).—  Mix  250  c.c.  of  HC1 
(specific  gravity  1.20)  with  750  c.c.  of  distilled 
water. 


The  Analysis  of  Spelter  131 

Method 

Place  25  grams  of  drillings  in  a  tall  500-c.c. 
beaker ;  add  250  c.c.  of  water  and  55  c.c.  of  HC1 
(specific  gravity  1.20)  and  stir.  When  the  action 
has  almost  ceased  add  more  acid  with  stirring, 
using  about  2  c.c.  at  a  time  and  allowing  to  stand 
after  each  addition,  until  finally  all  but  about  2 
grams  of  the  zinc  has  been  dissolved.  (Note  1.) 
Filter,  first  transferring  one  of  the  undissolved 
pieces  of  zinc  to  the  filter,  and  wash  twice  with 
water.  Discard  the  filtrate.  Wash  the  undissolved 
matter  on  the  filter  paper  into  the  500-c.c.  beaker, 
cover  and  dissolve  in  10  c.c.  of  water  and  10  c.c. 
of  HNO^  (specific  gravity  1.42).  Transfer  to  a 
casserole,  add  20  c.c.  of  H2S04  (1:1)  and  evap- 
orate until  fumes  appear.  Take  up  with  100  c.c. 
of  water,  boil,  cool,  and  let  settle  over  night.  (Note 
2.)  Filter  off  the  PbSO4  on  paper,  wash  twice  with 
water,  retain  the  filtrate  but  discard  the  paper  and 
precipitate.  Dilute  the  filtrate  to  400  c.c.,  add 
about  10  grams  of  NH4C1,  and  pass  H2S  gas 
through  for  1  hour  (Note  3).  Allow  to  stand  until 
the  precipitate  has  settled,  and  filter  off  the  im- 
pure CdS  (Note  4)  on  a  loose-bottom  Gooch  cru- 
cible. Eemove  the  precipitate  by  punching  out  the 
bottom  into  a  tall  200-c.c.  beaker,  wiping  off  the 
sides  of  the  crucible  with  a  little  asbestos  pulp. 
Add  60  c.c.  of  H,S04  (1 :5)  and  boil  for  30  minutes 
(Note  5).  Filter,  wash,  and  dilute  to  300  c.c.,  add 
about  5  grams  of  NH4C1  and  precipitate  with  H2S 
gas  as  before  (Note  6).  Repeat,  making  a  third 
precipitation  if  the  amount  of  cadmium  present  is 


132      Chemical  Analysis  of  Lead  and  Its  Compounds 

large  (Note  7).  After  the  final  precipitation,  let 
settle,  filter  and  transfer  to  a  weighed  platinum 
dish,  cover,  and  dissolve  in  HC1  (1:3).  Dissolve 
the  precipitate  remaining  on  the  paper  in  hot  HC1 
(1:3)  and  add  also  to  the  solution  in  the  platinum 
dish  (Note  8).  Add  10  c.c.  of  H,S04  (1:1)  and 
evaporate  the  solution  until  copious  fumes  are 
evolved  (Note  9).  Remove  the  excess  of  H2S04 
by  heating  the  dish  cautiously,  and  finally  heat  to 
between  500  and  600°  C.  Cool  and  weigh  as  CdS04. 

Notes. — 1.  The  addition  of  HC1  will  dissolve  the  zinc  and  a  small  amount 
of  the  cadmium.  By  adding  the  acid  in  small  quantities,  i.  e.,  keeping  the 
acidity  low,  and  also  keeping  the  solution  cold,  the  amount  of  cadmium  dis- 
solved will  be  small.  Since  it  requires  some  time  to  completely  reprecipitate 
any  cadmium  dissolved,  it  is  desirable  for  the  solution  to  stand  over  night 
following  the  addition  of  the  65  c.c.  of  HC1  at  the  start.  For  the  same 
reason  the  solution  should  be  allowed  to  stand  after  the  last  addition  of 
acid,  and  care  be  taken  that  the  stated  amount  of  spelter  remain  in  the 
undissolved  residue.  If  the  solution  is  heated,  or  if  time  is  not  allowed 
for  the  action  of  the  acid  to  cease  completely,  small  amount  of  cadmium 
may  pass  into  the  solution  and  be  lost. 

Equally  satisfactory,  or  in  some  cases  more  satisfactory  results  are  ob- 
tained by  using  ITSC^  to  dissolve  the  major  portion  of  the  zinc.  The  rate 
of  solution  is  slower  and  the  tendency  for  cadmium  to  pass  into  solution 
less.  The  quantity  of  acid  required  can  be  calculated,  measured  out  at  the 
beginning  and  small  quantities  added  from  time  to  time  as  the  action  be- 
comes slow. 

2.  It  is  desirable  to  allow   it  to  settle  over  night  to  precipitate  all  the 
PbSOi  from  the  solution  and  to  give  good  conditions  for  filtering. 

3.  It  is  occasionally  necessary  to  add  a  drop  or  two  of  ammonia  water 
to  the  solution  to  start  the  precipitation  of  CdS. 

4.  All  the  cadmium  will  be  precipitated  as  sulphide  together  with  some 
ZnS.     The  major  portion  of  the  zinc  will  remain  in  solution. 

5.  In  case  of  high  cadmium  content,  more  acid  may  be  required. 

6.  The  second  precipitation  should  give  practically  pure  CdS. 

7.  A  third  precipitation  will  remove  any  uncertainty  as  to  the  complete- 
ness of  the  separation  of  cadmium  from  zinc. 

8.  A  crucible  may  also  be  used  if  the  volumes  are  kept  small  or  evapo- 
rated before  transferring  to  the  crucible. 

9.  On  evaporating  to  fumes,  darkening  of  the  solution  may  occur  from 
filter  paper  shreds.     This  may  be  destroyed  by  diluting  slightly  with  water 
and  adding  5  c.c.   HNO3    (specific  gravity   1.42)    and   again  evaporating   to 
fumes. 


The  Analysis  of  Spelter  133 

Determination  of  Cadmium  by  the  Electrolytic 
Method 

Solutions  Required 

Potassium  Hydroxide  (Note  1). —  Dissolve  20 
grams  of  KOH,  c.  p.,  in  200  c.c.  of  distilled  water. 

Potassium  Cyanide  (Note  2). —  Dissolve  20 
grams  of  KCN,  c.  p.,  in  200  c.c.  of  distilled  water. 

Apparatus 

See  "Determination  of  Lead  by  the  Electrolytic 
Method." 

The  anode,  as  used  in  the  lead  determination, 
is  here  used  as  the  cathode,  and  vice  versa. 

Method 

See  "Determination  of  Cadmium  Gravimetri- 
cally." 

Dissolve  the  final  precipitate  of  CdS  in  hot  HC1 
(1:3),  boil  to  remove  H2S,  adding  a  few  drops  of 
HN03  (specific  gravity  1.42)  near  the  end,  and  fil- 
ter off  the  separated  sulphur.  Transfer  the  solu- 
tion to  a  200-c.c.  electrolytic  beaker,  add  a  drop 
or  two  of  phenolphthalein  and  then  KOH  solution 
until  a  permanent  red  color  is  obtained.  Add  KCN 
solution  with  constant  stirring  until  the  precipitate 
of  Cd(OH)2  is  completely  dissolved  (Note  3).  Di- 
lute to  150  c.c.  and  electrolyze  with  a  current  of 
five  amperes  for  two  hours  (Note  4).  Test  for 
completeness  of  deposition  by  washing  the  watch 
glasses  and  sides  of  the  beaker  to  increase  the 
depth  of  the  solution.  Continue  electrolysis  for 
twenty  minutes  and  if  the  newly  exposed  surface 


134       Chemical  Analysis  of  Lead  and  Its  Compounds 

of  the  cathode  is  still  bright,  remove  the  beaker 
with  electrolyte  and  wash  the  electrodes  three 
times  with  distilled  water  and  twice  with  ethyl 
alcohol  (95  per  cent).  Dry  the  cathode  at  100° 
C.,  cool  and  weigh.  The  increase  is  metallic  cad- 
mium. 

Notes. — 1.    Pure  NaOH  may  be  used  in  place  of  KOH. 

2.  Pure  NaCN  may  be  used  in  place  of  KCN. 

3.  Avoid  using  an  excess  of  KCN. 

4.  The  test  for  completeness  of  deposition  may   be  made  after  one  hour 
when  the  quantity  present  is  not  large. 


CHAfTEE  XIV 

STANDARD  METHODS  OF  CHEMICAL 

ANALYSIS  OF  ALLOYS  OF  LEAD, 

TIN,  ANTIMONY  AND  COPPER1 

These  methods  apply  particularly  to  white  metal 
bearing  alloys  (known  commercially  as  "Babbitt 
Metal")  and  to  similar  lead  and  tin  base  alloys. 

Two  sets  of  methods  are  here  given.  The  first 
method  is  somewhat  slow  but  is  recommended  as 
giving  the  more  accurate  results  where  the  analysis 
of  these  alloys  is  of  comparatively  infrequent  oc- 
currence. The  second  method  is  rapid  and  is  suit- 
able for  control  work,  giving  good  results  after  the 
analyst  has  become  familiar  with  it. 

I.   GENERAL  METHOD2 

A.   Determination  of  Lead,  Copper,  Antimony 
and  Tin 

Determination  of  Lead 
Solutions  Required 

Mixed  Acid.—  Dissolve  20  grams  of  KC1  in  500 
c.c.  of  water,  add  400  c.c.  of  HC1  (specific  gravity 
1.20),  mix  and  add  100  c.c.  of  HN03  (specific  grav- 
ity 1.42). 

iReprinted  by  permission  from  the  1921  Book  of  A.  S.  T.  M. 
Standards  of  the  American  Society  for  Testing  Materials. 

2G.  W.  Thompson's  method.  See  Journal,  Soc.  Chem.  Ind.  Vol. 
15,  p.  179. 

135 


136       Chemical  Analysis  of  Lead  and  Its  Compounds 

Alcohol  Hydrochloric  Acid  Mixture. —  Mix  400 
c.c.  of  95  per  cent  ethyl  alcohol  and  100  c.c.  of  HC1 
(specific  gravity  1.20). 

Acid  Ammonium  Acetate. —  To  500  c.c.  of 
NH4OH  (specific  gravity  0.90),  add  500  c.c.  of 
water  and  then  acetic  acid  (80  per  cent)  until 
slightly  acid  to  litmus. 

Method 

Dissolve  1  gram  of  the  finely  divided  alloy  by 
boiling  in  70  to  100  c.c.  of  "mixed  acid"  solution 
in  a  covered  beaker.  Add  more  "mixed  acid"  if 
a  complete  solution  of  the  alloy  is  difficult  to  obtain, 
and  continue  boiling  until  evaporated  to  about  50 
c.c.  Add  5  c.c.  of  HC1  (specific  gravity  1.20),  cool 
in  ice  water  until  the  bulk  of  PbCL  has  crystallized 
out,  then  add  slowly,  with  constant  stirring,  50  c.c. 
of  alcohol  (95  per  cent),  continue  stirring  for  a 
few  minutes  and  cool  in  ice  water  for  10  minutes. 
Add  50  c.c.  more  alcohol  from  a  pipette,  allow  to 
stand  in  ice  water  for  20  minutes  and  filter  through 
9-cm.  paper  into  an  800-c.c.  beaker.  Wash  by  de- 
cantation  three  times  with  alcohol  hydrochloric 
acid  mixture  and  finally  wash  the  paper  twice  with 
the  same  mixture.  Wash  the  PbCL  from  the  paper 
back  into  the  beaker ;  wash  paper  several  times 
with  hot  water,  catching  washings  in  beaker  with 
the  bulk  of  the  chloride.  Finally  wash  paper  with 
hot  ammonium  acetate  solution.  Heat  until  all 
PbCL  is  dissolved.  Add  15  c.c.  of  saturated  solu- 
tion of  KoCr.Or ;  heat  until  precipitate  is  of  good 


The  Analysis  of  Alloys  137 

orange  color;  filter  on  weighed  Gooch  crucible; 
wash  with  water,  alcohol  and  ether;  dry  at  110° 
C.  and  weigh.  Calculate  percentage  of  lead  by  the 
empirical  factor  of  63.75. 

Notes. — 1.  With  proper  manipulation,  the  PbClo  precipitate  should  con- 
tain consistently  all  but  0.003  grams  of  lead. 

2.  During  the  heating  of  the  acid  ammonium  acetate  to  dissolve  the 
PbCl«,  the  solution  should  remain  perfectly  clear,  any  turbidity  indicating 
the  presence  of  tin  or  antimony,  as  even  1  milligram  of  tin  or  antimony  will 
cause  a  slightly  but  distinct  turbidity. 

Determination  of  Copper  and  Antimony 
Solutions  Required 

Potassium  Hydroxide. —  Dissolve  100  grams  of 
KOH  in  500  c.c.  of  water. 

Potassium  Cyanide. —  Dissolve  3.5  grams  of 
KCN  in  1800  c.c.  of  water  and  standardize  against 
copper  of  known  purity. 

Sodium  Thio sulphate. —  Dissolve  24.8  grams  of 
Na2S203.5H20  in  1000  c.c.  of  water,  and  allow  to 
stand  for  24  hours.  Standardize  against  Anti- 
mony Metal,  c.  p.,  using  same  quantity  of  reagents 
and  same  procedure  as  under  (c)  Determination 
of  Antimony. 

Method 

See  " Determination  of  Lead." 

Evaporate  the  filtrate  from  PbCL  filtration  by 
boiling  in  the  loosely  covered  800-c.c.  beaker,  and 
finally  take  to  dryness  on  a  water  bath.  Add  10 
c.c.  of  KOH  solution  and  after  a  few  minutes  add 
20  c.c.  of  3  per  cent  H2O2.  Add  more  KOH,  if 
solution  is  acid,  until  an  alkaline  reaction  is  shown 
by  litmus  paper.  Heat  on  the  water  bath  for  20 


138      Chemical  Analysis  of  Lead  and  Its  Compounds 

minutes,  add  10  grams  of  ammonium  oxalate,  10 
grams  of  oxalic  acid,  and  200  c.c.  of  water  and  heat 
to  boiling.  Pass  in  ILS  for  45  minutes  with  solu- 
tion near  boiling ;  filter  at  once ;  and  wash  precip- 
itate with  hot  dilute  solution  of  oxalic  acid  satu- 
rated with  H2S,  catching  washings  with  filtrate. 

Wash  the  precipitate  of  copper  and  antimony 
sulphides  from  the  filter  paper  back  into  the  beaker 
with  the  least  amount  of  water  possible ;  treat  with 
10  c.c.  of  KOH  solution;  heat  on  water  bath  until 
the  undissolved  matter  is  distinctly  black,  filter 
through  same  paper  into  a  300-c.c.  Erlenmeyer 
flask.  Wash  the  precipitate  with  hot  water  con- 
taining a  small  amount  of  K2S. 

(a)  Determination  of  Copper  by  Potassium  Cyanide 

Titration 

Dry  and  ignite  the  precipitate  with  paper  in  a 
small  casserole,  dissolve  in  nitric  acid  (specific 
gravity  1.42),  boil  to  expel  nitrous  fumes,  neutral- 
ize with  Na2C03,  add  a  few  drops  of  NH4OH  and 
titrate  with  standard  KCN  solution. 

(b)  Determination  of  Copper  by  Electrolytic  Method 

See  "Determination  of  Copper  by  Potassium 
Cyanide  Titration." 

Dry  and  ignite  the  sulphide  precipitate  in  a  small 
casserole,  dissolve  in  10  c.c.  of  HNO3  (specific  grav- 
ity 1.42),  boil  until  oxides  of  nitrogen  are  expelled 
and  add  50  c.c.  of  distilled  water.  Transfer  to  a 
tall  200-c.c.  beaker,  wash  out  casserole,  add  5  c.c. 
of  H2S04  (specific  gravity  1.84)  and  determine  cop- 


The  Analysis  of  Alloys  139 

per  by  electrolysis.  See  the  determination  of  cop- 
per by  the  electrolytic  method  in  the  Standard 
Methods  of  Chemical  Analysis  of  Manganese 
Bronze  (Serial  Designation:  B  27)  of  the  Ameri- 
can Society  for  Testing  Materials. 

Notes. — 1.  On  filter  after  heating  with  KOH  solution,  the  copper  remains 
as  sulphide  with  a  small  amount  of  lead  sulphide  which  failed  to  be  pre- 
cipitated as  chloride.  If  it  is  desired  to  determine  this  lead,  it  can  be  done 
by  separation  from  the  copper  by  ordinary  methods. 

2.  If  the  amount  of  antimony  and  copper  is  small    (less   than   10  milli- 
grams)   the  lead  which  failed   to  be  precipitated  as   chloride  may   also   fail 
to  come  down  as  sulphide  on  passing  HL,S  through   the  oxalic  solution.     It 
will  remain  in  the  filtrate  from  the  sulphides  and  be  deposited  electrolytic- 
ally  with  the  tin  on  the  cathode.     This  can  be  prevented  by  adding  an  oxalic 
acid  solution  of  a  pure  antimony  salt  containing   about   100   milligrams   of 
antimony  just  before  passing  HL,S.     In   this  case  antimony   must  be   deter- 
mined on  a  separate  portion. 

3.  If  the  amount  of  copper  present  is  from  8  to  10  milligrams  or  more, 
it  should  be  determined  by  the  electrolytic  method.     In  this  case  the  small 
amount    of    lead    precipitated    as    sulphide    with    the    copper    is    deposited 
on   the   anode  as   PbOo   and   may   be   weighed,   calculated   to   lead  by   factor 
86.43  and  added  to  that  obtained  under  "Determinations  of  Lead." 


Determination  of  Antimony 

See  "Determination  of  Copper  by  Potassium 
Cyanide  Titration." 

Add  50  c.c.  of  HC1  (specific  gravity  1.20)  to  the 
KOH  solution  of  antimony  sulphide,  and  boil  down 
to  small  volume  until  all  arsenic  has  been  expelled 
as  arsenious  chloride. 

Add  25  c.c.  of  HC1  (specific  gravity  1.20)  and  1 
gram  of  KC1O3  and  boil  until  colorless.  Filter  into 
a  300-c.c.  Erlenmeyer  flask,  through  glass  wool  if 
sulphur  has  separated,  wash  out  original  flask  with 
HC1  (specific  gravity  1.20),  cool,  add  1  gram  of 
KI,  1  c.c.  of  CS2,  and  titrate  with  standard  thio- 
sulphate  solution. 


140      Chemical  Analysis  of  Lead  and  Its  Compounds 

Determination  of  Tin 
Apparatus  for  Electrolysis 

Electrodes. —  Cylindrical  cathodes  of  platinum 
wire  gauze,  2  by  1%  inches  diameter. 
Platinum  wire  spiral  anodes. 

Method 

See  "Determination  of  Copper  and  Antimony. " 

Concentrate  the  filtrate  and  washings  from  the 
precipitated  sulphides,  if  necessary,  to  a  volume 
of  200  c.c.  and  add  5  grams  more  of  oxalic  acid  in 
case  the  amount  of  tin  is  over  0.5  gram.  Electro- 
lyze  until  the  solution  reacts  alkaline,  using  a  cur- 
rent of  about  0.5  ampere.  Remove  the  cylinder; 
wash  twice  with  distilled  water  and  once  with  95 
per  cent  ethyl  alcohol ;  dry  at  110°  C.  and  weigh. 

Note.— If  the  electrolysis  is  carried  out  over  night  it  will  usually  be  found 
by  morning  that  the  solution  has  become  alkaline  and  it  may  be  taken  for 
granted  that  the  tin  has  all  been  precipitated  on  the  cathode.  The  best 
results  are  obtained  by  regulating  the  current,  or  the  time,  so  as  to  render 
the  solution  alkaline  only  a  very  short  time  before  the  cathode  is  to  be 
removed.  The  cathode  should  be  placed  close  to  the  bottom  of  the  beaker 
to  insure  proper  agitation  of  the  electrolyte. 

B.   Determination  of  Arsenic 

Solutions  Required 

Ferric  Chloride. —  Solution  of  specific  gravity 
1.43. 

Ammonium  Carbonate. —  Dissolve  75  grams  in 
500  c.c.  of  water. 

Method 

Weigh  1  gram  of  sample  into  a  250-c.c.  distilla- 
tion flask  and  add  10  c.c.  of  FeCl:{  solution,  60  c.c. 
of  HC1  (specific  gravity  1.20),  20  c.c.  of  water  and 


The  Analysis  of  Alloys  141 

5  grams  of  KC1.  Connect  the  flask  with  a  con- 
denser, heat  slowly  until  solution  is  complete  and 
boil  down  to  as  small  a  volume  as  possible^  catch- 
ing distillate  in  a  tall  400-c.c.  beaker.  Cool  flask, 
add  50  c.c.  HC1  (specific  gravity  1.20)  and  redis- 
till as  before,  catching  distillate  in  same  beaker. 
Cool  distillate  and  pass  H2S  through  for  one  hour, 
allow  to  settle  and  filter  the  arsenious  sulphide  on 
a  Grooch  crucible.  Wash  twice  with  HC1  (1:4), 
four  times  with  cold  water,  three  times  with  alco- 
hol and  four  times  with  CS2.  Dry  at  110°  C.  for 
10  minutes,  and  weigh  after  cooling.  Dissolve  the 
arsenious  sulphide  with  (NH4)2  C03  solution,  wash 
thoroughly  with  water,  dry  for  30  minutes  at  110° 
C.  and  reweigh  after  cooling.  The  difference  in 
weights  multiplied  by  0.60911  gives  the  percentage 
of  arsenic. 


II.   RAPID  METHOD  FOR  CONTROL 
WORK1 

A.    Determination  of  Lead  and  Copper 

Solutions  Required 

"Lead  Add."—M.ix  300  c.c.  of  H,SO4  (specific 
gravity  1.84)  and  1800  c.c.  of  distilled  water.  Dis- 
solve 1  gram  of  lead  acetate,  c.  p.,  in  300  c.c.  of 
distilled  water  and  add  this  to  the  hot  solution, 


3See  "The  Analysis  of  Alloys  of  Lead,  Tin,  Antimony  and  Copper,"  by 
D.  J.  Demorest,  Journal  Ind.  and  Eng.  Chem.,  Vol.  V,  p.  842  ;  "Rapid 
Analysis  of  Alloys  for  Tin,  Antimony  and  Arsenic,"  by  F.  A.  Stief,  Journal 
Ind.  and  Eng.  Chem.,  Vol.  VII,  p.  211  ;  and  "Technical  Analysis  of  Brass," 
1917.  Price  and  Meade,  p.  182. 


142      Chemical  Analysis  of  Lead  and  Its  Compounds 

stirring  meanwhile.     Let  stand  at  least  24  hours 
and  siphon  through  a  thick  asbestos  filter. 

Dilute  Alcohol  for  Washing. —  Mix  equal  parts 
of  denatured  alcohol  and  distilled  water. 

(a)  Determination  of  Lead 

In  a  covered  300-c.c.  Erlenmeyer  flask  dissolve 
1  gram  of  the  alloy  in  20  c.c.  of  H2SO4  (specific 
gravity  1.84) ;  heat  the  solution  nearly  to  boiling 
until  the  metal  is  completely  decomposed  and  the 
PbS04  is  white  (this  may  take  30  minutes  or  more) 
and  finally  boil  for  several  minutes.  Allow  to  cool, 
but  not  below  60°  C.,  and  then  add  slowly  50  c.c. 
of  water  while  the  solution  is  agitated.  Heat  to 
boiling  for  several  minutes  in  order  to  insure  com- 
plete solution  of  antimony  sulphate.  Allow  the 
PbS04  to  settle  out  until  the  solution  is  clear,  not 
letting  the  temperature  fall  below  60°  C.  If  the 
liquid  does  not  clear  quickly  it  must  be  heated 
longer.  When  clear,  pour  solution  through  a 
weighed  porcelain  Gooch  crucible  with  asbestos 
mat,  decanting  the  solution  as  completely  as  pos- 
sible without  allowing  more  than  a  very  small 
amount  of  PbS04  to  go  over  into  the  crucible.  Now 
add  10  c.c.  more  of  H2S04  (specific  gravity  1.84) 
to  the  PbS04  in  the  original  flask,  and  boil  for  sev- 
eral minutes.  Cool,  add  slowly  30  c.c.  of  water, 
and  again  heat  to  boiling  for  a  few  minutes ;  allow 
the  solution  to  cool  to  about  60°  C.  and  completely 
transfer  the  PbS04  to  the  Gooch  crucible.  Wash 
with  lead  acid,  retaining  the  filtrate  and  these 
washings  for  the  copper  determination.  Remove 
the  beaker  containing  these  solutions  and  wash  out 


The  Analysis  of  Alloys  143 

the  lead  acid  with  dilute  alcohol;  set  the  Gooch 
crucible  inside  a  porcelain  crucible ;  dry  and  ignite 
for  five  minutes  at  the  full  heat  of  a  Tirrill  burner ; 
cool  and  weigh  as  PbS04,  which  contains  68.29  per 
cent  lead. 

(b)  Determination  of  Copper 

To  the  filtrate  from  the  PbS04,  which  contains 
the  copper  and  which  has  been  transferred  to  an 
Erlenmeyer  flask,  add  NH4OH  (specific  gravity 
0.90)  until  the  solution  is  slightly  alkaline;  then 
add  2  c.c.  of  H2S04  (specific  gravity  1.84) ;  heat 
nearly  to  boiling;  add  2  grams  of  Na2S03  and 
when  this  is  entirely  dissolved  add  1  gram  of 
KCNS  dissolved  in  10  c.c.  of  water.  Shake  well 
and  allow  the  precipitated  CuCNS  to  settle  for  one 
hour  while  the  solution  is  kept  hot.  Filter  on  a 
close  filter  paper,  wash  with  cold  water  and  ignite 
paper  and  precipitate  in  a  porcelain  crucible.  Pro- 
ceed by  one  of  the  two  following  methods : 

(1)  Dissolve  in  HNO3   (specific  gravity  1.42), 
add  5  c.c.  H2S04  (specific  gravity  1.84),  evaporate 
until  fumes  of  H2S04  are  evolved.    Dilute  to  about 
100  c.c.  with  distilled  water.    Add  1.5  c.c.  of  HNO;J 
(specific  gravity  1.42)  and  determine  copper  by 
electrolysis.     See  the  "Determination  of  Copper 
by  the  Electrolytic  Method, ' '  Standard  Methods  of 
Chemical  Analysis  of  Manganese  Bronze  (Serial 
Designation:   B  27)  of  the  American  Society  for 
Testing  Materials. 

(2)  Dissolving  the  ignited  precipitate  in  HNO;! 
(specific  gravity  1.42),  as  in  (1);    boil  to  expel 


144       Chemical  Analysis  oj  Lead  and  Its  Compounds 

nitrous  fumes,  neutralize  with  Na.COs  and  deter- 
mine volumetrically  with  cyanide  as  in  A  of  ' '  Gen- 
eral Method. " 

Note. — If  the  amount  of  copper  is  very  small  it  may  escape  detection  by 
this  method,  in  which  case  it  should  be  determined  as  in  A  of  "General 
Method." 


B.   Determination  of  Arsenic,  Antimony 
and  Tin 

Apparatus 

Arsenic  Still. —  A  condenser  is  made  from  glass 
tubing  in  the  form  of  a  letter  S,  about  18  in.  long 
and  Vi>  in-  in  inside  diameter,  tapering  to  about 
Yi  in.  at  the  upper  end  and  to  about  %  in.  at  the 
lower  end.  One  curve  is  nearly  filled  with  water, 
and  is  submerged  in  cold  water  in  a  500-c.c.  beaker. 
The  lower  end  dips  into  about  75  c.c.  of  water  in  a 
300-c.c.  beaker  and  the  upper  end  is  connected  by 
a  delivery  tube  with  a  300-c.c,.  Florence  flask,  closed 
with  a  rubber  stopper  which  is  fitted  with  a  deliv- 
erjr  tube  and  with  a  thermometer  reaching  to  about 
1  in.  above  the  surface  of  the  liquid  in  the  flask. 

Solutions  Required 

Iodine. —  Dissolve  10.7  grams  of  iodine  in  50 
c.c.  of  distilled  water  which  contains  20  grams  of 
KI  in  solution  and  dilute  to  1000  c.c.  with  distilled 
water.  Standardize  against  pure  tin  having 
exactly  the  same  conditions  for  titration  as  are 
specified  for  the  analysis  of  the  alloy.  Each  cubic 
centimeter  is  equivalent  to  approximately  0.00500 
gram  of  tin  or  0.00315  gram  of  arsenic. 


The  Analysis  of  Alloys  145 

Potassium  Permanganate. —  Dissolve  2.7  grams 
of  KMn04  in  distilled  water,  filter  through  asbes- 
tos, and  dilute  to  1000  c.c.  with  distilled  water. 
Standardize  against  pure  antimony  having  exactly 
the  same  conditions  for  titration  as  are  specified 
for  the  analysis  of  the  alloy.  Each  cubic  centi- 
meter is  equivalent  to  approximately  0.00500  gram 
of  antimony  or  0.00465  gram  of  iron. 

Ferrous  Ammonium  Sulphate. —  Dissolve  12.4 
grams  of  ferrous  ammonium  sulphate  crystals  in 
950  c.c..  of  distilled  water  and  add  50  c.c.  of  H2S04 
(specific  gravity  1.84). 

Starch. — To  1000  c.c.  of  boiling  water,  add  a 
cold  suspension  of  6  grams  of  starch  in  100  c.c.  of 
distilled  water;  cool,  add  a  few  drops  of  chloro- 
form and  mix  thoroughly. 

(a)   Determination  of  Arsenic 

In  a  300-c.c.  Florence  flask,  dissolve  0.5  gram 
of  the  alloy  in  exactly  8  c.c.  of  H2S04  (specific 
gravity  1.84).  The  metal  must  be  finely  divided, 
preferably  in  the  form  of  thin  foil  like  shavings, 
although  sawings  or  very  fine  drillings  may  be 
used.  Heat  the  solution  to  boiling ;  cool,  add  about 
5  c.c.  of  water  and  a  bulk  of  about  0.5  c.c.  of  clean 
granulated  pumice  stone  and  boil  the  covered  solu- 
tion very  gently  for  about  five  minutes,  or  until 
the  strong  odor  of  S02  can  no  longer  be  detected. 
Finally,  being  careful  to  have  5  c.c.  of  water  pres- 
ent, cool  the  solution  to  about  18°  C.  and  cautiously 
add  20  c.c.  of  HC1  (specific  gravity  1.20).  Insert 
in  the  flask  a  rubber  stopper  fitted  with  a  thermom- 


146       Chemical  Analysis  of  Lead  and  Its  Compounds 

eter  and  delivery  tube  and  connect  the  delivery 
tube  with  the  "S"  condenser.  Heat  the  solution 
to  gentle  boiling  for  from  10  to  15  minutes,  keep- 
ing the  vapor  temperature  at  107°  C.  for  at  least  5 
minutes.  Wash  out  the  condenser  into  a  300-c.c. 
beaker  and  add  an  excess  of  about  2  grams  of 
NaHC03.  Bring  the  volume  of  the  solution  to 
about  200  c.c. ;  warm  to  about  27°  C.  and  titrate 
with  standard  iodine  solution  and  starch  to  the 
appearance  of  a  deep  blue  color. 

Note. — A  blank  determination  should  be  made  on  corresponding  amounts 
of  reagents  treated  as  above,  and  the  results  should  be  corrected  accordingly. 

(b)  Determination  of  Antimony 

Cool  the  solution  which  remains  in  the  flask  after 
the  arsenic  distillation ;  add  about  130  c.c.  of  cold, 
recently  boiled  distilled  water,  to  which  has  been 
added  about  3  c.c.  of  HC1  (specific  gravity  1.20) 
and  titrate  with  standard  KMnO4  solution  to  the 
appearance  of  a  decided  permanent  pink  color. 
From  a  burette  add  an  excess  of  standard  ferrous 
ammonium  sulphate  solution  until  the  pink  color 
is  discharged  and  then  titrate  with  standard 
KMn04  solution  to  the  reappearance  of  a  pink 
color. 

(c)  Determination  of  Tin 

If  the  sample  does  not  contain  14  per  cent  (or 
0.07  gram)  of  antimony,  add  enough  dissolved 
SbCl3  to  the  solution  to  bring  the  contents  of  anti- 
mony up  to  about  0.07  gram  for  the  purpose  of 
insuring  perfect  reduction  of  the  tin  and  uniform 
conditions  for  the  titration.  Then  add  exactly  6  c.c. 


The  Analysis  of  Alloys  147 

of  H2S04  (specific  gravity  1.84)  and  60  c.c.  of  HC1 
(specific  gravity  1.20)  and  add  about  6  in.  of  clean, 
soft  No.  14  pure  iron  wire  cut  into  2  in.  lengths 
and  cleaned  with  dilute  HC1  just  before  using. 
Boil  gently  for  30  minutes,  add  about  6  in.  more 
wire  and  boil  30  minutes  longer.  Remove  from 
heat,  close  flask  loosely  with  a  rubber  stopper  and 
allow  about  two  minutes  for  all  air  to  be  expelled 
by  hydrogen  and  acid  vapors.  Close  flask  tightly 
and  quickly  place  it  in  cold  water,  cooling  the  solu- 
tion to  about  20°  C.  Transfer  the  solution  quickly 
to  a  500-c.c.  beaker  (leaving  the  iron  wires  in  the 
flask)  and  rinse  flask  and  contents  with  150  c.c. 
of  cold,  recently  boiled  distilled  water.  Add  rins- 
ings to  main  solution  in  the  beaker,  bring  final 
volume  to  about  300  to  350  c.c.  and  titrate  quickly 
with  standard  iodine  solution  and  starch  to  the 
appearance  of  a  strong  blue  color. 

Note. — A  blank  determination  should  be  made  on  corresponding  amounts 
of  reagents  treated  as  above,  and  the  results  should  be  corrected  accordingly. 

If  the  copper  content  of  the  alloy  is  as  high  as  about  3  per  cent  or  over, 
it  prevents  a  good  end  point  in  the  tin  titration  when  the  tin  percentage  is 
low.  Under  such  conditions,  just  before  titrating,  add  about  1  gram  of  KI 
crystals,  stir  until  nearly  dissolved  and  titrate  immediately.  If  allowed  to 
stand  too  long  at  this  point,  trouble  may  be  encountered,  due  to  the  precipi- 
tation of  some  of  the  constituents. 

Other  forms  of  pure  iron  may  be  employed,  but  the  wire  as  above  specified 
has  been  found  convenient. 

For  accurate  work  it  is  desirable  to  reduce  and  titrate  the  solution  of  tin 
in  an  atmosphere  of  CO2. 


CHAPTER  XV 

PHYSICAL  PROPERTIES  OF  PIGMENTS 

Determination  of  Apparent  Density 
The  determination  of  the  apparent  density  and 
fineness  of  lead  compounds  has  lately  become  of 
special  importance  in  many  laboratories  where  it 
is  essential  that  the  physical  properties  of  these 
compounds  be  under  control.  The  method  must 
combine  accuracy  and  rapidity.  While  many 
methods  have  been  suggested  for  such  control,  it 
has  been  found  that  when  rapidity  is  required  the 
most  excellent  results  are  obtained  through  the 
determination  of  the  weight  of  a  cubic  inch  of  the 
compound.  This  weight  is  dependent  on  two  fac- 
tors, the  fineness  and  the  density  of  the  particles. 

The  determination  is  carried  out  on  a  Scott 
volumeter,  modified  by  replacing  the  funnel  hav- 
ing a  fixed  wire  screen,  with  a  funnel  having  an 
elongated  neck,  so  arranged  as  to  allow  the  use 
of  various  mesh  silk  bolting  cloth.  See  Fig.  3. 
While  not  only  allowing  of  numerous  determina- 
tions of  fineness,  the  difficulty  encountered  through 
particles  of  the  compound  adhering  to  the  wire 
screen  is  eliminated. 

The  apparatus  consists  of  a  stand,  A,  on  which 
is  mounted  a  small  tower,  B,  containing  baffle 
plates  of  glass  which  serve  to  evenly  distribute  the 
compound  under  examination.  The  funnel  is 
divided  into  two  sections,  one  the  funnel  proper, 
D,  and  the  other  the  neck,  E,  which  fits  over  the 

148 


Physical  Properties  of  Pigments  for  Tests  149 


FIG.  3.    Modified  Form  of  Scott  Volumeter. 


150       Chemical  Analysis  of  Lead  and  Its  Compounds 

funnel  proper  and  holds  the  silk  bolting  cloth 
firmly  in  place.  The  metallic  cube  is  exactly  one 
cubic  inch  in  size. 

The  mesh  cloth  most  suitable  for  the  compound 
on  which  the  determination  is  being  made  is  fast- 
ened in  the  funnel.  It  has  been  found  that  a  No.  9, 
Standard  Silk  bolting  cloth  which  has  about  97 
meshes  to  the  inch  gives  concordant  results,  it  being 
of  such  coarseness  as,  in  most  cases,  to  allow  all 
the  compound  to  be  brushed  through  the  cloth.  The 
cube  is  placed  directly  under  the  baffle  plates,  the 
compound  is  placed  in  the  funnel  and  gently 
brushed  through  until  the  cube  is  entirely  filled. 
By  a  rapid  stroke  with  a  spatula  the  excess  of  the 
compound  is  removed,  leaving  an  even  cubic  inch 
of  the  material.  The  cube  and  its  contents  are  then 
weighed  and  the  weight  of  the  cube  deducted, 
giving  the  weight  of  a  cubic  inch  of  the  compound. 
Several  determinations  should  be  made  and  an 
average  should  be  taken.  Results  may  be  obtained 
by  this  method  which  vary  not  more  than  y2  of  a 
gram.  In  the  hands  of  different  analysts  it  has 
been  found  that  results  may  vary  more  than  this, 
due  to  the  personal  equation  in  the  carrying  out  of 
the  method;  however,  the  method  is  only  a  com- 
parative one  and  enables  any  analyst  to  closely 
check  the  apparent  density  of  compounds  in  a  very 
rapid  manner. 

The  laboratory  of  the  Willard  Storage  Battery 
Company  has  improved  the  Scott  Volumeter  by 
attaching  an  electric  buzzer  to  the  side  of  the  volu- 


Physical  Properties  of  Pigments  for  Tests  151 

meter.  This  buzzer  is  operated  when  a  gram 
weight  determination  is  being  made  and  renders 
results  more  accurate  in  that  it  prevents  any  of  the 
pigment  adhering  to  the  glass  baffles. 

"Gram  Weight." — If  the  weight  of  the  cubic 
inch  of  pigment  is  determined  in  grams  the  result 
is  called  the  "  gram  weight"  of  the  pigment. 

Color,  Color  Strength,  Coarse  Particles 

In  making  determinations  of  these  physical 
properties  of  pigments  the  analyst  should  use  the 
methods  as  outlined  in  the  Circular  of  the  Bureau 
of  Standards,  No.  85,  on  "Recommended  Speci- 
fications for  Basic  Sulphate  White  Lead,  Dry  and 
Paste,7'  as  found  on  page  15. 

Oil  Absorption1 

The  oil  absorptive  property  of  pigments  is  a 
physical  property  that  is  often  measured  and  the 
best  results  can  be  obtained  only  by  adhering 
closely  to  the  method  of  Gardner  and  Coleman.1  A 
brief  summary  of  the  most  important  details 
follows. 

Weigh  20  grams  of  dry  pigment,  free  from 
lumps,  and  place  in  a  400-c.c.  beaker  or  round  bot- 
tom jelly  glass.  Drop  raw  linseed  oil  slowly  from 
a  burette  onto  the  pigment,  carefully  lifting  the  pig- 
ment with  a  spatula  until  all  the  pigment  has 
become  wet  with  oil.  Stirring  or  otherwise 
bringing  pressure  to  bear  on  the  pigment 

iPapers  on  Paint  and  Varnish,  Gardner. 


152      Chemical  Analysis  of  Lead  and  Its  Compounds 

should  be  avoided.  As  the  end  point  is  approached 
the  pigment  will  gather  in  small  balls.  Finally  the 
small  balls  will  unite  in  one  large  one  which  will 
flatten  out  in  the  bottom  of  the  glass  into  a  sticky 
mass.  This  is  the  end  point.  The  number  of  cubic 
centimeters  of  linseed  oil  multiplied  by  five  gives 
the  amount  of  oil  required  for  100  grams  and  this 
is  taken  as  the  oil  absorption  figure. 


INDEX. 

A. 

Page 

Acetic  acid,  in  basic  carbonate  of  lead 91 

Navy  method 92 

Thompson's  method 91 

Acid  ammonium  acetate  solution 23 

Alloys,  of  antimony,  tin,  lead  and  copper 135 

Alloys — rapid  method  for  control 141 

Antimony— 

in  alloys 135-137,  139 

in  pig  lead 118 

Ammonium  molybdate  method  for  lead 1 

Apparent  density,  determination  of 148 

Arsenic — 

in  alloys 144 

in  antimony  alloys 135,  144 

in  pig  lead 114 

B. 

Barium  chloride  solution 24 

Barium  sulphate  in  lithopone 48 

Basic  carbonate  of  lead,  analysis  of 89-108 

composition  of 96 

recommended  specification,  Bureau  of  Standards .  97 

Basis  sulphate  of  lead,  analysis  of 9,  16 

composition  of 9 

recommended  specification,  Bureau  of  Standards.  12 

Bichromate  method  of  lead 3 

Bichromate  solution 23 

Bismuth,  in  lead Ill 

Brushing  properties  of  lithopone  paint 50 

153 


154  Index 

r\ 

Page 

Cadmium — electrolytic  method  for 133 

in  pig  lead 118 

in  spelter 130 

Calcium,  interference  of,  in  molybdate  method 3 

Calculation,  lead  contents  of  sublimed  white  lead .  .  18,  27 

Calculations  for  lithopone 56 

Caking  in  container 19 

Carbon,  in  sublimed  blue  lead 34 

Carbonic  acid,  in  basic  carbonate  of  lead 94,  102 

Carbonate  of  lead,  in  sublimed  blue  lead 34 

Chart  for  rapid  analysis  of  red  lead 69 

Coarse  particles  in  pigments 15 

Cobalt,  in  pig  lead 123 

Color,  of  pigments 14 

Color  strength  of  pigments 15 

Colorimetric  method  for  copper  and  iron 59 

Composition  of  sublimed  white  lead 9,  27 

Copper,  colorimetric  method  for 59 

electrolytic  method  for 138 

potassium  cyanide  method  for 138 

Copper,  in  alloys 135,  137,  141 

in  litharge 60,    87 

in  pig  lead 60,  119 

in  red  lead 62 

Copper  sulphate,  standard  solution 62 

Corroded  white  lead,  analysis  of 89 

recommended  specification  for,  Bureau  of 

Standards..  97 


D. 

Bichromate  solution,  preparation  of 23 


Index  155 

Page 

Electrolytic  deposition  of  lead 109,  126 

of  cadmium 133 

of  copper 138 

Extraction  mixture  for  oil  in  paste  paints 25 

F. 

Fatty  acids,  preparation  of 20 

Ferrous  ammonium  sulphate  solution 4 

Flake  red  lead,  analysis  of 72 

G. 

"Gramweight "  of  pigments 151 

H. 

Hanus  solution 25 

Hydrogen  peroxide,  standard  solution 67 

I. 

Iodine  number  of  fatty  acids 22 

Iodine  solution,  preparation  and  standardization  of. .  144 

lodometric  method  for  tin 146 

arsenic  in  lead 145 

Iron,  colorimetric  method  for,  in  oxides  of  lead 59 

Iron,  in  litharge 86 

in  orange  mineral 62 

in  pig  lead 122 

in  red  lead 62 

in  spelter 129 

in  sublimed  white  lead 12 

in  zinc . .                                                                    .  129 


156  Index 

Page 

Lead,  bichromate  method  for 3 

Lead  contents  of  sublimed  white  lead,  a  calculation..     27 

Lead  in  alloys 135,  141 

Lead,  in  spelter,  lead  acid  method 127 

electrolytic  method 126 

Lead,  in  sublimed  blue  lead 32 

Lead,  in  sublimed  white  lead 9,  10,  16 

bichromate  method 10 

calculation  of 18,  27 

molybdate  method 10 

sulphate  method 5,    89 

Lead,  in  zinc 126,  127 

Lead,  interference  in  colorimetric  methods 64 

Lead,  molybdate  method  for 1 

Lead,  free  metallic,  in  litharge 85 

Lead  dioxide,  analysis  of 66 

Lead  ores 1 

Lead  oxide,  in  sublimed  white  lead 18,  27 

in  sublimed  blue  lead 34 

Lead,  pig,  A.  S.  T.  M.  method  for Ill 

Lead  sulphide,  in  sublimed  blue  lead 33 

Lead  sulphite,  in  sublimed  blue  lead 33 

Lead  sulphate,  in  sublimed  white  lead 9,  17,  27 

in  sublimed  blue  lead 33 

in  zinc  oxide 35 

Lead  total,  in  basic  carbonate  white  lead 89 

in  sublimed  white  lead 10,  16 

Litharge,  analysis  of 85 

composition  of 85 

Lithopone,  anatysis  of 48,  53 

composition  of 48 

recommended  laboratory  examination 49 

fastness  to  light 51 


Index  157 

M. 

Page 

Manganese,  in  pig  lead 123 

Mineral  oil,  test  for 22 

Moisture,  in  litharge 85 

in  paste  paints 19 

in  pigments 16 

in  red  lead 66 

Molybdate  method  for  volumetric  determination  of 

lead 1 

N. 

Nickel,  in  pig  lead 123 

Non-volatile  vehicle  in  lithopone  paints 52 

0. 

Oil  absorption,  of  pigments 151 

Orange  mineral,  analysis  of < 66 

composition  of .....'. 66 

Organic  color,  in  orange  mineral 74 

in  red  lead 74 

P. 

Paste  paints,  laboratory  examination  of 19 

Physical  properties  of  lithopone 50 

Physical  properties  of  pigments 148 

Physical  tests  for  pigments 148 

Pigments,  percentage  in  paints 19 

Pig  lead,  analysis  of Ill 

Potassium  bichromate  method  for  volumetric  deter- 
mination of  lead 3 

Potassium  ferrocyanide  method  for  volumetric  deter- 
mination of  zinc 6,  17?  23 

Potassium  ferrocyanide,  standard  solution  of 6,  23 

Potassium  Iodide  solution 25 

Potassium  permanganate,  preparation  and  standard- 
ization of  solution  of .  .  71 


158  Index 

Page 

Red  lead,  analysis  of 66,  75 

Red  lead,  recommended  laboratory  examination  of, 

Bureau  of  Standards 74 

Red  lead  content  of  litharge,  orange  mineral  and  red 

lead 66,  75 

Red  lead,  composition  of 66,  75 

Running,  of  paints 77 

8. 

Sampling  of  pigments,  dry  and  in  paste 98 

Scott  volumeter 149 

Silica,  in  litharge 88 

in  lithopone 54 

in  red  lead 74 

Silver,  in  lead  ores 7 

in  pig  lead Ill 

Skins  in  paste  paints 23 

Smith's  method  for  electrolytic  deposition  of  lead.  .  .  109 

Sodium  hydroxide  solution,  aqueous 25 

alcoholic 26 

Sodium  oxalate,  standardization  of  potassium  per- 
manganate with 71 

Sodium  thiosulphate,  preparation  and  standardiza- 
tion of  standard  solution  of 24 

Specification,  recommended  by  Bureau  of  Standards 

for  sublimed  white  lead  dry  and  paste 12 

Spelter,  analysis  of,  by  A.  S.  T.  M.  standard  method  125 

Standardization  of  ammonium  molybdate  solution.. .  2 

of  potassium  ferrocyanide  solution 6,  23 

of  potassium  permanganate  solution 71 

of  sodium  thiosulphate  solution 24 

Starch  solution 25 

Streaking,  of  paints 77 


Index  159 

S — Concluded.  _> 

Page 

Sagging,  of  paints 77 

Sublimed  blue  lead,  analysis  of 32 

composition  of 32 

lead  carbonate  in 34 

Sublimed  white  lead,  analysis  of 9,  16 

composition  of 9,  27 

recommended  specification,  Bureau  of  Standards.  12 

Sulphate,  lead,  in  sublimed  blue  lead 33 

in  sublimed  white  lead 9 

Sulphate  method  for  lead 89 

Sulphide,  lead,  in  sublimed  blue  lead 33 

Sulphite,  lead,  in  sublimed  blue  lead 33 

Sulphur,  total,  in  sublimed  blue  lead 32 

in  zinc  oxide 36 

T. 

Thompson's  method  for  acetic  acid 91 

Tin,  in  alloys 135,  140,  144 

electrolytic  method  for 140 

in  pig  lead 118 

Total  lead,  in  sublimed  blue  lead 32 

in  sublimed  white  lead 10,  16 

Typical  analysis  of  basic  carbonate  of  lead 96 

U. 

Unsaponifiable  matter,  test  for 43 

Uranyl  indicator  for  zinc  titration 7,  23 

V. 

Volatile  matter,  in  sublimed  blue  lead 34 

in  basic  sulphate  white  lead  paste 19 

Volatile  thinner,  in  lithopone  paints 51 


160  Index 

V — Concluded. 

Page 

Volumetric  methods  for  lead- 
bichromate  method 3 

molybdate  method 1 

Volumetric  method  for  zinc;  ferrocyanide  method .  6,  17,  23 

W. 

Walker  method,  for  basic  carbonate  of  lead 89 

Water,  in  lithopone 51 

Water  soluble  content  of  zinc  oxide 36 

Water,  soluble  matter,  in  red  lead 76 

Weight  per  gallon,  lithopone  paints 50 

Z. 

Zinc,  in  lead  ores .  .  6 

in  pig  lead 122 

Zinc,  metallic,  analysis  by  A.  S.  T.   M.   standard 

method 125 

Zinc  oxide 35 

Zinc  oxide,   recommended  laboratory  examination, 

Bureau  of  Standards 37 

Zinc  oxide,  in  sublimed  blue  lead 34 

in  sublimed  white  lead .  11,  17 

Zinc,  potassium  ferrocyanide  method  for 6,  17,  23 

Zinc  sulphide,  in  lithopone 49 

Zinc  sulphate,  in  zinc  oxide 36 


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